Gus Potter

Yes, you're right James. Some deflection takes place as you add say masonry which is a constant load, call this a dead load. The rest comes from say floor / roof loading which is variable load, call this a live load. Thus you have the "intial" deflection from the dead load. Then a variable deflection from the live load. Generally we assume for most domestic applications say using steel lintels that the deflection response is linear up to a point. Thus your total deflection is the sum of the dead + live load deflections. Precambering is an option but for the self builder just needing the odd beam it can be a bit costly. Best if you can to just make the beam/ lintel say a bit bigger. As Peter says (I think) if you have too much deflection, intial or otherwise you can just create something that does not look good. Too much and even the best door mastic operative will not be able to hide a significant downwards bow! Spot on Mike..go for bottom supported as the doors (glass mainly) are heavy and introduce a fair bit of variable load to a lintel as they open and shut.

Good point Peter. SillyBilly looks like there is more to this than meets the eye. If the wall is going to be an internal wall at the end of the day then why lightweight insulating blocks? Is there an issue with the founds say and you are trying to reduce the loading? The wall looks like it is 6.3m long , usually after about 6.0m you start to worry about significant shrinkage cracking in cement based blocks (as opposed to clay), assuming the materials have been looked after and the mortar mix is not too strong. Even with walls shorter than this you get some shrinkage cracks around the opening depending on the surrounding wall geometry. Much also depends on the wall height, geometry and how the SE say has designed it. Vertically spanning, two way spanning and so on. To give you relevant pointers then a drawing or two would help. If you are just worried about the wind loading in the temporary condition then your starting point is this. If you look at the probability of the wall being loaded by the wind over a two year period then the wind loading is reduced (by some 35 to 40 %) as the normally calculated wind loading is usually based on a 50 year return period. But the wall may have been designed with a certain amount of compression, say from the upper floors / roof. Often if you have a good weight on a wall then compression is beneficial as it counteracts the tension stress developed on one face of the wall by the sideways wind loading. On the practical side you could consider introducing a couple of temporary wind posts on the outside of the wall, you may have the space to do this. We know that aerated type blocks are hard to get a good fixing to so when you are building the wall introduce some bent leg tie straps with a twist. The bent leg would turn down the inside face of the wall and where the strap comes out the outside face you have the twist. Now screw fix the strap to the side of your wind post, go for timber posts. Fix the posts top and bottom. When ready remove the temporary timber wind posts and recycle. The bed reinforcement looks great on paper but for a brickie it's another hassle and makes it harder to keep the coursing level. If you really need it SE wise then fine but the brickie will charge you more to bed it and for the extra time they will have to take to get everything level. You also have the cost of the bed reinforcement and time to procure. If you're laying the blocks your self then make sure you have a practice with bed reinforcement as although the flattened type S/steal stuff looks great it still makes it harder to maintain level coursing if you are working on a 10.0 mm mortar bed and standard units sizes. If you deviate from this then you'll often find that you can't marry up the wall coursing where it ties into other walls. Hope this gives you a few ideas.

Hello Moggaman. Working on the basis that your purlins are supported somewhere along the span? maybe a splice? below is part of a steel spec. "All steelwork is to be fabricated by a CE approved fabricator and comply with the BS EN 1090 series requirements. Site welding is not permitted. It is the Contractor's responsibility to check all steelwork dimensions prior to manufacture." "Shot blast to grade SA2.5 and painted with a zinc rich primer. Nominal DFT 80 microns." Shot blasting comes in varying degrees of "cleaning", SA2.5 is a common one for domestic applications. The primer spec gives your local fabricator a bit of play as to what they can use.. the tins of paint are actually drums of paint so they can "use up a drum" on your job. DFT means nominal dry film thickness.. in other words it looks like paint not just a sniff. It's worth doing as a matter of good practice and can help protect vulnerable parts like the welds and bolts / fixings. In summary, if your steel is in an indoor, heated and fully protected and non aggresive environment then strictly speaking no need for painting / treatments. If it is running over a bathroom and you may have moisture? Would I leave the steel raw on my own house? No. The primer can get rubbed a bit as it's quite soft so don't panic if you see a few bits scuffed off. Last thought, it often comes in two colours, red or grey if that matters?

Hello flanagai. It may be that an SE say or an Architect that has a good SE background is best placed to help here. At some point some calculations may be required for BC purposes if you encounter the unexpected. If you think about it this way. You'll be doing the rest from underbuilding up. The groundworks could be considered as a stand alone package. You are already "project managing" it. You can do a lot to help yourself and keep the cost down. Let's say you engage a local contractor to lay the founds and take the underbuilding up to wall plate level. To price this they will take your drawings, work out the amount of dig and muck away, the volume of concrete, amount of say blocks, wall ties and the amount of say lean mix cavity fill you need. Somewhere they often say.. "based on the drawings" Now for the self builder one problem that arises is if you need to make the founds deeper, say you hit a soft spot. In some case the founds need to be shallow if you encounter rock. Let's take the deeper as more common. Here you have many options; use say trench fill, just make the founds thicker using higher grade concrete if not that much, lay the foundations deeper and make the under building higher. However, there comes a point where your masonry wall thickness needs to be increased if it gets too deep, this is partly to do with the soil pressure on the side of the walls under the ground. All of a sudden things can grow arms and legs. Here an SE type person is often best placed to advise on the most economic option. What you can do is ask the contractor to give you a price based on the drawings but also give you rates for say extra dig, cost per square metre of each masonry leaf. Break this down into a cost say for up to 900mm below working site ground level and up to 1500mm below ground level. Also ask for rates to support the ground if you need to go deeper. Basically ask for rates for extra work. Now, if it turns out once you have excavated the ground that you need to do more work then you have a set of agreed rates. This can transfer more risk to you but you have more control. On the other hand you can just say to the contractor.. you take all the risk.. but you will pay for this.. very rarely will the contractor be the looser here. This is where an SE can really help. Get them in early and they will help you identify what rates you need to get in terms of extra work. Once you have set this up you should often be able to measure up your self and agree the payments. Now let's say you do need to do extra work. The SE will have a discussion with you and the builder and say here is the most economic way of overcoming the unforseen. In summary doing it this way will result in you paying for what you get.. often no more and if you all get on ok and you pay your bills on time you may get a bit extra for free as you'll know. For all, many contractors like working for good reasonable and fair clients so will occasionally go a bit less heavy on the invoicing.

Hi Jack. If fixing to a slab then "underhanging" removes issues of the reduced edge fixing distance, that being the distance from the fixing into the concrete to the edge of the concrete. If over hanging then this problem arises. At 10mm variation between the high point and low point you are in the ball park regarding mortar bedding thickness. If you have 5.0mm mortar bed at the high point then you'll end up with 15mm thickness of bed at the low point.. all within acceptable limits. The following is based on the assumption that you have not cast the slab to high! If you have then that is for another day. Enough of the theory! ..some practical stuff. Here is a method of bedding a wall plate to get a quality job. The first thing is that timber is not straight when you lay it down on site.. it may have been when it left the merchants! Lay your wall plate down on plan and it will often have a bow, look at it sideways on elevation and it will be bowed that way too. And just to add to the dilemma it will also often be twisted. Usually you have a DPC between the timber and the slab. Staple the DPC to the bottom of the soleplate. Next get some wet timber, say 100 x 22 mm soft wood. Rip this down lengthways so you have little strips of different thicknesses, say 4 x 22 , 6 x 22 , 8 x 22 and so on. Cut these into 150mm lengths.. like kindeling for the fire. Put the sole plate on the slab, pilot drill it so the screw can slip freely and part fix it down to the slab with say 120 mm x 5mm screws and plugs. As you do this get the sole plate as straight as you can on plan. Often you only need screws at 900 to 1200 mm centres so it's not to onerous to do. Also, you can use the screws to take the twist out as you can either put them close to the edge of the slab or more inboard. Fine to do as they are just temporary fixings and non structural. Now work your way along it putting in the timber packers to get the top level. Try as best you can to keep the packers away from the stud positions. You'll not always get this bang on so don't worry. Just don't put them where you have a cluster of studs say taking high loads from lintels etc above or too close to the corners. You need to slacken and retighten the screws as you go to get the packers in. You'll not get it perfect but do the best you can. Once you have got it all as straight as you can unscrew the sole plate, put down the mortar bed and reposition the screws. Slowly tighten the screws while giving the top of the timber a tap down with a hammer. Leave it all to set. After a few days of dry weather the packers will shrink and you can wiggle them out easily. Point up the small holes they leave. Don't use dry timber for the packers as it will swell and lift the sole plate.. and you won't get them out later. Leave the screws in place as this helps keep the sole plate in place while you are putting up the kit. Once the kit is up follow the SE's instructions for permanant holding down fixings and so on. For all. The above is a bit lengthy but if you are self building and ordering a kit (TF) the manufacturer will often have a clause in their spec about how level the sole plate has to be. Deviate from this and it can let them shift the blame to you if something is not quite right with the kit. If you are going traditional masonry construction then you may have a trussed rafter roof. Again, the wall plate tolerances are covered in the manufacture's clauses. Traditionally, less so now we used to make the bedding of the wall plate part of the brickies work package, particularly in Scotland when doing TF. This gives a clear line of demarcation. Brickies are not so keen on this now as.. All the best Jack and hope this helps, or you can adapt the above principles to suit your slab.

Hi Jack1962. As a general rule of thumb. Mortar bedding should be between 5 and 20mm thick. Less than 5mm and the bed is too thin, more than 20mm and the mortar will start to crack, shrink, loose strength as it's too thick. Sole plates need to be evenly bedded so you can see that at less than 5mm thick they will also be hard to gently tamp down to level (like bedding a brick), more than 20mm and the mortar will start to just spill out of the bed. The mortar will tend to be less compacted at the edges and more in the middle so the sole plate will want to twist (rock) one way or the other. Also, once you exceed 20mm of mortar you can impact on the performance of any fixings holding down the sole plate. The other thing to look out for is how much the sole plate is overhanging say masonry below. Generally for a 90 -100mm wide sole plate you want it over / underhanging by no more than 12mm. For a 140 - 150mm sole plate no more than 20mm. If you exceed this then a number of issues arise. The first is that the sole plate can load the supporting structure below (say masonry) eccentrically (usually not about it's centre of gravity) and this can introduce unwanted bending type forces, local over stressing in the masonry for example. Again you can have an issue with the fixings as if the timber is too far overhanging the fixings can end up too close to the edge of the timber / masonry / concrete and thus become less effective. If your masonry is well off being flat (level along the top) then if you get really stuck you can use an extra sole plate that is fixed to the masonry on some bedding to partly sweeten it out. Then put another sole plate on top which is packed with structural packers. Each solution needs a bit of thought as one size does not fit all build methods. Just be aware that timber shrinks quite a lot perpendicular to the grain so the more horizontal timbers you introduce the more vertical shrinkage you'll get. this may or may or be an issue. If your walls are just not straight on plan then? each case needs assessed. If you have a variation of 5mm over 5.0m then it looks like the brickie / person preparing the support for the sole plate has done a pretty good job!

Hello Tank. To get the best out of Build Hub you can try doing a quick sketch on a bit of A4 showing the ground level, your foundation etc. Don't worry about the quality.. no one will slag you off for a bad drawing..you need to see some of mine! Take a photo of your page and post it. Sometimes it's easier to make a drawing than to try and explain it in writing. The main thing is to have a bit of fun posting on BH and don't worry about using "technical" speak..just spill it out! I'm guessing but have you a found and you are trying to work out how you lay the masonry so that when you get out the ground the brick / block courses are level? If this is the case.. (most founds are not that flat and level) then for example you can lay concrete blocks "on the flat" which is the wide side down and adjust the mortar bed thickness..aiming to keep the mortar thickness to less than 20mm.. does not always work in practice for DIY but that is the aim. If you have not done it before it takes a bit of thinking out.. but great when you get it right!

Belt and braces..to add Squirt some expanding foam into the joints between the gaps, tape it up (plenty info on BH about cheep effective tapes) as the foam is not that vapour tight but really helps keep the insulation in place. Sleep tight.. and.. in the winter; don't put on 5 gallon pots of stock on the stove steaming away all night, avoid drying vast amounts of washing without opening the windows. It's you own home so you know to let the "steam out"..just be sensible. Keep the heating on at low so you get some residual heat permeating though to the outside walls and into the roof space, you move the dew point outwards and you'll be fine. In terms of heating cost, it's a few quid extra a year?, no point in analysing this to death as you have a refurb /conversion. Just do your reasonable best and march on! Start thinking about the kitchen units and the enjoyable stuff! In other words don't go away for example, let the place freeze, come back and make lots of water vapour. It's like an old car with leather seats, they crack if you keep them in an old damp garage, take it out and crank up the heater.

Yes putting the insulation under the slab is fine. What you are doing is bringing the slab into the inside of the insulation envelope, just like if you have some masonry walls inside. In some ways you have a big storage radiator (hate to say it but often called thermal mass) which can help stabalise the temperature in the room. It's important that you carry the insulation below the slab up the sides so you "wrap" it fully in the insulation blanket. There are practical benefits in that you often have something more solid to lay your floor on and build non load bearing partition walls off.

Hello Laurence. I would start by asking the builder to confirm what lintel they put in. Next step, if different from spec just drop the SE a note to say.. for example.. due to supply constraints the builder swapped the lintel for a xyz type... as said builder was trying to help out.. is this OK? and include a few photos. Many SE's are sympathetic and will go the extra mile to review. As a word of encouragement. It looks like from the photos that the lintel is carrying mostly the dead weight of the blocks rather than the weight of the blocks plus a variable load (live / imposed load.. say a snow load on the roof) so most of the deflection could already have taken place. Thus when you measure for the doors you'll take the smallest dimension off a datum.. usually in the middle if the lintel has been installed level. I'm being cautious here as there could be a load on the inside leaf we can't see from the photos.. if this differs a lot from the outer leaf load then you'll find in the detailed manufacturer's notes a reference to what is call the "load ratio". This is the difference between the inner and outer leaf loads. If the two say go beyond a 3:1 ratio it can make the declared load capacity invalid. Hence my suggestion to contact the SE just in case. Folk on BH have different views on support beams over bifolds / large span sliding doors. Cold formed steel lintels such as Catnic / Keystone and others are absolutely fine in the right circumstances so long as you know how to design them and also very importantly make sure they are installed correctly as per the instructions. With a 2.5m bifold you should be well within the region where a Catnic or similar will be fine. Yes, cold formed steel lintels are attractive as they can be cheeper and help with thermal bridging, but they a more complex beast.. Laurence the standard of workmanship on the blockwork could be better.. but I would like to see the whole wall inside and out before making further comment. Let your SE see this as they will want to look at things in the round. The main thing is don't panic and think it has to come down! If it is an issue there are many work around solutions. For the very curious.. sizing Catnic / Keystone lintels and similar products for bifolds. Yes there is no doubt that folk have issues with these cold formed steel lintels. A Universal beam is a steel beam that is rolled into shape when the steel is still hot. It starts off as a big lump of hot metal and is rolled in it's "hot" state. Roughly, a cold formed steel section starts as a big lump of hot metal that is rolled into a big toilet roll, a standard roll weighs about 6-7 tonnes from memory. This roll goes to say Catnic, they unroll it and shape it using a series of rollers into their lintel section when the steel is cold. But these two different processes result in the steel behaving in a different way. Cold formed lintels can be more complex to install depending on their shape and if they are supporting just the outer leaf of masonry or both. if you are say a designer and want to use a Catnic type lintel over bifolds you can do a back calculation. Lets say you have a span as in Laurence's case of 2500mm. Now deep in the technical spec may be something that says "deflection limit is based on span / 360" This means that one of the criteria is that the total deflection should not exceed 2500/360 = 6.9mm.. Often ok for bifolds particularly if you have more "dead" load that bends the lintel before you get the doors measured up. But say you have a span of 3600 mm. Now here you take 3600 / 360 = 10mm.. This is a recognised deflection limit in the codes.. but for bifolds in particular you may be starting to push your luck. Remember that in general DIY / self builders have less control over the standard of workmanship. What an SE/ Designer can do is to say.. we are not happy with manufacture's deflection limits. We know that this lintel is certified for X amount of load at a deflection limit of span/360 = 10mm .. lets make sure that we size the lintel based on 80% of the declared load and all other things being equal (lintel bearing etc) we are now on the ball park to getting a deflection of roughly 80% of 10mm = 8mm and this we can live with in terms of door design. If you read this far.. thanks!

Me too! Loz.. don't panic, could well be a bit of site / delivery damage.. however something like that will not look sweet over you doors if it's more than a couple of mm. It looks like the roof joists are not spanning onto the lintel? If so the loading could just primarily be from the few courses of block above. If you are rough casting the block you could bring a bellcast bead down just below the edge of the lintel and this would hide the bit that is bent and improve the drip over the doors. Just have a quick check to make sure that if the builder has swapped the lintel type it is still ok to use for the load.

Hello SillyBilly. Well done picking up on the arrangement and timber sizes. In pic two at the top of the thread you can see there is a gap between the outer ply and the two inner ones. Now it may be that the two inner timbers are enough to carry the load and the outer one is just a "filler". But when you design timber lintels you can "enhance" the strength and stiffness in recognition that the plys are acting compositly.. together. For example in the BS code you can increase the capacity of the timbers in bending say by ~10% and the stiffness of 3 plys by ~21%. The "strength" part is to do with making sure the timber does not "break" under load".. the stiffness property (Young's modulus.. E) is to do with how much the timber will bend. Members posted a while ago about this and deflections over the heads of bifolds / sliding doors a while ago in the thread " Issues with sliding doors" Some of that post be be of use to you. Link here The key here is to recognise that to get an extra bang for your buck the lintels need to be fixed together (no gaps) say with 4.5 x 100mm galvanised nails top middle and bottom at 300mm horizontal centres. If you are using say a C16 / 24 timber grade then the overall thickness will be ~ 135mm and as Russell says you can use a timber ripping on the inside to make the wall flush on the inside for the plasterboard. This is common practice. If your flat roof joists don't span onto the timber lintels then 3 ply 225 x 45 timbers effectively spanning say 2.8m ( 2.7 + 1/2 rest) supporting say typically a 1.0m wide strip of flat roof (only) has a good chance of working with an over all deflection of some 6mm. Some of that will take place under the self weight of the roof before you fit the doors, the rest due to roof access loadings, snow and a bit of creep in the timber.

Moonshine. Our posts overlapped. moonshine "its too late for us, as we are committed to traditional footings at the top." How far on are you..? maybe a design review could be in order. "when i spoke to him previously he said that is what it says in the building regs, i presume that the loading on the retaining wall" 0 out of 10 to the SE for that response... very poor if that is all you got. If the SE had taken the time to explain to you over the phone (would take less than 5 - 10 minutes) the ins and outs then you would not feel the need to post!

It's a detail with many facets. Hard to make constructive comment without more info, particularly on the soil, how far you are from the boundary and so on. In some ways this can be quite clever. Here the SE may be using the steps to create a safe excavation. The SE may be backfilling with a material that loads the basement wall less so you make a saving here. You have beam and block floor so that affords a good stiff point to connect the basement wall into at the top so you can design it as a propped cantilever... again potential savings. I have done a remedial job where you backfill with EPS blocks on the outside so you load the basement wall with very little lateral earth loads. The reason for this is that the lateral earth pressure loads need to go somewhere else after they are transferred to the basement wall... long storey.. best left. I think there is more to this than meets the eye. Interested to see how this develops.

Have you expressed your view to these Architects? If so, have you had a response? Keep us posted.

Yes it does seem like a bit of a pile on. Unfair in my view. If you are a first time self builder on a budget then perhaps look for experience coupled with practical knowledge about buildability and associated costs. Many of the professions: Technician, Architect, SE cross fertilise and as these folk go through their career they become modestly competant in each other's disciplines. All these designers can deliver good value if you are in the right frame of mind. I work with a Chartered Architect who has a great feel for the SE side.. but has been at it for forty years and worked with countless SE's. If you have a larger design budget and want something unique then a good Architect can often deliver something special. To do this they will often pull together an SE and Architectural technologist who have the same frame of mind. They all work as a team. The design cost will increase but you get the full breadth of experience.

Good points from all. The geology of Lincolnshire is quite variable, some expensive to build on ground, great ground too and stuff in the middle. This is where you can get tripped up. Try and find out as much as possible about the ground as this could have a big influence on the design if you are on a tight budget. The other thing in Linconshire is flood risk.. have a read around this and see if this could throw up a design issue. Have quick look here for an educational resource and if you feel able then provide more info on your site. http://mapapps.bgs.ac.uk/geologyofbritain/home.html In some ways you can get quite far managing the cost risk but if you don't spend a bit of time researching the ground then you always have that big elephant in the room that can stop you enjoying the journey as much as you could be. It's often said that if you are building on the ground then what lies underneath often poses the biggest cost risk. At the concept stage try and spread your research time so you cover all the elements of the build rather than focusing too much on say the choice between timber frame and masonry construction. @hbooth If your not sure about the geotechnics / ground then just post on BH and you'll get plenty help.

Hi SaveaSteading. Your approach is much appreciated and interesting. Hope this helps. The geology of the Highlands is unique and fascinating. Here are some avenues and my thoughts on how you could continue to explore this. Some may well not apply to you but BH is a journey! Say you look at this in the context of a two supply system. One supply is for the bogs and watering the plants when the good dry weather comes, the other for drinking / washing water. You mention an ample burn and that it may have a journey before it gets to you.. say past a few silage pits, crofts and other folk's septic tanks ,which have yet to be upgraded. If many of the old septic tanks etc upstream have been upgraded (wishful thinking) this only tends to reduce the BOD (biological oxygen demand) but not the pathogens and other undesirable chemical compounds so much. However, the water that falls on your garden will generally make its way to the burn . You could maybe dig a relatively shallow trench that intercepts the surface ground water flow in your garden as it travels towards the burn. In other words your garden acts as a partial filter. In a dry summer it may be that the flow is reversed to some extent. Here your garden would act to partially filter the water as it makes it's way from the burn to the trench. In other words during a dry summer you still get more rain on the higher ground so even if your water table drops locally in your garden you can still draw off a sensible amount of water from the burn. When the next winter comes the flow is reversed back to the burn so your garden filter could be "self cleaning". This is how a sand filter in a sewage treatment plant works to some extent. I digress a bit here but it's worth a mention for other BH members too. SUDs requirements. There are a good few posts on BH about this and folk are aware that it relates to say flood prevention. However, there is another aspect to this. If you have dry spell of weather then contamination can build up on your roof. Many industrial buildings have roofs that are plastic (say) coated and the UV sun rays degrade this. Also, you get birds nesting and so on. If you then get a short burst of rain you wash a high concentration of contamination into a burn / stream that is at a low flow level. You don't get the dilution and this kills the fish and other organisms. Saveasteading.. the same principle could apply in your case. If you are on the West coast of Scotland you'll get more frequent rain.. but the East can be very dry for a few months. If you can find a way of storing enough drinking water/ washing for the dry months then you could in principle be drinking the best water in the world! Once you work your way through this then you can weigh up the economics / practicality of boreholes / spring supply (reliability / security of supply as not on your land) vs say harvesting. Have a look at how you can get rid of your waste water. Mortgage.. maybe some lenders will pick up on the fact that you have an unusual scheme. If you present a good technical case and compare with say a bore hole that may choke up in ten / twenty years time then it's food for thought. One avenue is to show that your scheme complies with the current regs, say in terms of a potable supply of water. From a pratical point of view if your borehole pump breaks down then they are nearly impossible to recover.. I have seen them stuck fast after a few weeks! You often can't get them back out and you have a cable in the way plus a steel recovery wire, try getting a same sized pump back down the same hole! You could get all this to work out with a fair wind. If you wish then post more info about what you know about the ground, the slope, geometry of your plot ect. Your geotechnics and topography could well be a key here to getting this to work.

Hello all. By all means explore using this material, I'm all for using new technology.. it's not that new. There are recognised design codes that cover this material. For the self builder.. a practical point. Using say FRP (Basalt say) rebar for an external "non structural slab" may well be cost effective if just laid in flat sheets. To get the best out of it you need to control the other parameters.. compaction, selection of the concrete type and strength, preparation of the sub base, the extra support to maintain the concrete cover etc..it does not corrode but if the cover varies too much you get uneven stresses in the slab which will promote cracking. This may put your local builder off or they may add a bit to the price. If you are using it say in a structural concrete beam or a basement then you'll often need some bent bars. FRP bends need to be formed in the factory.. you have no wriggle room. Thus if you don't get all your setting out absolutely spot on you have trouble ahead. Steel rebar can be "tweeked" a bit on site.. FRP? You may say.. well.. that is up to the builder to get it right.. you can but this will come at a cost.. For the technically curious. When you design say a reinforced concrete beam subject to downards loading you often aim to design the rebar as the "weakest link". Steel (in the tension zone of a beam) will stretch (yield) quite a lot before it fails. On the top of the beam the concrete is in compression. When concrete fails in compression it is a much more sudden (explosive) failure. In summary one thing you do is to make sure that if a reinforced concrete beam / slab is over loaded then the occupants of a building get some warning.. big cracks appearing etc. You achieve this by taking advantage of the ductility property of the steel once it reaches it's yield point. Ductility and elasticity are two different properties. But FRP (Basalt say) does not have quite the same forgiving nature to some extent as common structural steel / rebar. Once steel starts to yield it can "stretch" quite a bit before it fails. In fact with common structural steel you get a little extra out of it before really bad things start to happen. With FRP it is appreciated that you may get some yielding but often not as much as say with steel. Once you take this safety aspect into account (which you have to do to comply with the building regs in terms of structural design for domestic structures say) and look at things in the round then the difference between the two materials becomes less marked. If you are considering using this for your build then it's worth a bit of research to check that while the big easy areas look good price wise you are not making a rod for your back later.. say with corners / beams or reducing the number of contractors you can go to to get a good price.

Hi Bramco. Have a look at your soil report. It may mention what is called the soil shrinkage potential also known as the volume change potential. This a rough estimate on how much it will shrink and swell between say winter and summer.. it can be very little or a lot. Here is a link to the NHBC guidance, plenty diagrams etc to give you a feel for things. https://nhbc-standards.co.uk/4-foundations/4-2-building-near-trees/4-2-10-heave-precautions/ There is a bit on how trees can influence the design. Once you have got the basics, then you should be better placed to look at identifying a good solution particular to your site, recognising that you have a stiffer "crust" over a softer layer. For plenty of domestic stuff ground bearing type slabs can be made to work above an allowable bearing capacity of 50 kPa without spending a fortune. It's the swelling / shrinkage and things like trees that can put a bit of a spanner in the works.

Hello all. As George says it's an interesting material, the price is coming down due to volume etc so can be an attractive option for the self builder. I can see why SE's are cautious.. for a reason. As an overview we can see that say the Orlitech bars have a significantly higher tensile strength than steel rebars. ~ 2-4 times say so you can see how they are "stronger". But they are much more stretchy! This is reflected in what is called the modulus of elasticity.. Youngs modulus. Ordinary steel rebar has a modulus of elasticity of say 205 GPa while these types of glass/ basalt/silica based bars have a Young's modulus of say 60 - 90 GPa. So they are say 2 -4 times more stretchy.. elastic. This elasticity is important for concrete design as the concrete has to move more before the bars take up the same load as a similar sized steel bar. Thus you have to be aware that you could either get bigger cracks.. or more of them. If you are doing a basement that needs to keep water out then crack control can be essential. If you are say designing a beam then the beam will deflect more before the bars take up the load. Again this needs some thought. In the main you can increase the diameter of the bar (or use more of them) to mitigate the deflection.. and this impacts on the economics. @kxi Here Kxi is doing an external slab say. Often you may use say a A142 mesh with sawn joints say every 4 -6 m depending on the geometry for a hard standing area. The larger the area of the slab between the joints often the heavier mesh. These sawn joints encourage the shinkage to take place at the joint where you don't see it and this leaves the slab looking good.. if you have taken care laying it, the sub base and curing it properly. If you use a more stretchy mesh, Basalt say, then you may get more cracking where you don't want it. In simplistic theory you could argue that if you have a ground bearing slab resting on a very very slippy DPM then it should behave a bit like a steel reinforced ground bearing slab when curing and shrinking.. but it will be more flexible when you come to run a few waggons over it. Thus it may not last as long? Kxi.. by all means use it for your external slabs or the drive, it will be a bit of an experiment to some extent. The key to getting this to work is careful and exact preparation of the sub base, get it evenly compated.. as level as you can, use a plastic DPM so as the concrete shrinks it can easily slip about so that the movement takes place at the edges or at the joints.

It can be if you know how to go about it. You use basic trigonometry to do it. Onoff.. you can cheat and model it in 3D to check the maths. As an aside having visited a few precast outfits they use an almost dry sand / cement toner mix and mechanically whack that into the mould in layers. It's not like concrete we pour for founds say. If you want to copy what the precasters do then I think getting a really sturdy mould (shutter) is one key. I have seen the precasters using the expensive pigmented mix next to the shutter and no pigmented stuff in the middle. That said I have cast chimney copes say in ordinary concrete hand batched in a half bag Belle mixer and carried up in pails with a drip and a good DPC under.. I passed one the other day and it's still looking good after 25 years..but my glasses are a lot thicker these days. If your DIY precast cill is a bit permeable then make sure you spend time getting the DPC all neat and water tight.

On paper it looks like a nice neat concept in part..but.. I wonder how much horizontal load they can take. When the wind blows you can generate some 100 -150 kg/square metre ball park wind force say on the sides of the building. I had a quick look at the brochure and they show a timber structure with a shallow pitch roof. These types of roof can generate quite a bit of uplift and really need to be well tied down. When you couple the uplift with the horizontal load one might conclude that you have a building on roller skates. I wonder if there is some detailed load tables available for example that cover the above? Extensions are a substancial investment. Don't skimp on the founds. Once you dig deeper into this you may well find that if you are using SIPS panels say you need something heavy in the ground to fix to, stop them overturning / lifting up anyway. Going for a light weight found could make a rod for your back later.

Thanks volcane, dp and Peter for reading. When I was doing the formula bit I thought readers would loose the will to live!

Jeremy. That's a nice looking gable, bit of brick detail and loads of garden trees by the looks of things. The garden / trees look full of potential to have fun. Peter et al have posted some info on the "Heritage House" link below previously and there are threads on BH that discuss various details. https://www.heritage-house.org/damp-and-condensation/managing-damp-in-old-buildings.html Have a read at this. My own view is that while informative they are punting their own business / academic credentials.. so I take some of the stuff with a bit of salt. One thing is that if you over insulate the bathroom you could shift the dew point inwards..the point that water vapour starts to condense. It may be worth while using a bit less insultation in the bathroom external wall.. not super insulate it. Compensate for this loss of insulation elsewhere.. the rooms that have less moisture. But before you do all of this have a good look at the pointing on the external walls, the mortar, ground levels and external drains. gutters and down pipes etc. No point in doing all this internal insulating and upgrading if you don't let the building breathe on the outside. All the best and look forward to seeing how you get on.