Gus Potter

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.

Interesting thread this. Good technical points made by Peter,Craig et al. To add my thoughts, partly technical, but mainly to open up design options you can consider that are cost effective, that won't lead to problems with your mastic etc on the finishes, sticky door issues, glass that fails due to adverse unforseen loads etc and the subsequent arguments. Don't forget that these large glazed openings cost a lot, the glass, slim frames etc. A bit of technical stuff. The formula for deflection of a steel beam is 5* w* L^4 /384 EI. For the keen, often domestic steel beam design ignores what is called shear deflection but for timber beams this needs to be accounted for as it is significant. To explain the formula for typical domestic steel beams. E is Young's modulus.. a property of the steel which does not change with beam size. w is the load per metre run of the beam. I is what is called the second moment of area and L is the length. Now you can see that if E, I and w all stay the same then if you have a beam 3.0m long then L is to the power of four i.e. 3*3*3*3 = 81 units, if you have a four metre beam we have 4*4*4*4 = 256 Now 256 divided by 81 = 3.16. So you get over 300% more deflection on a four metre beam than one that is 3.0m long all other things being equal. The thing to draw from this is that beam deflections are very sensetive to length. Extrapolate this to an 6-8m opening and you get this exponential deflection which plays havoc with your doors. The next parameter you can vary is the second moment of area "I". To get your head around this the formula for a rectangular beam is I = b*d^3 / 12 where b is the width and d is the depth. You can see here that if you have a rectangular beam 200mm deep beam d^3 (cubed) is 200*200*200 = 8*10^6 mm^3 (mm cubed) but if you have a same width but 300mm deep it is 300*300*300 = 27*10^6mm^3. So buy increasing the depth of the beam by 100mm you reduce the deflection by 27/8 ~ 300%. The way a steel I beam works is that you cut out the sides and place more steel in the flanges. This give a much more efficient shape so by moving the material to the top and bottom flanges you get more "I" for your buck! Now for a big glazed opening design the starting point is how much deflection will be ok over the head of the doors. There are general structural recommendations in the codes that go along the lines of beam span / 360 but these are mainly to do with the other elements of the building. If you have an effective clear span of 8.0m that is 8000mm / 360 = 22mm. That is going to jamb your doors, break the mastic seal (at times you will notice the bend over the opening) on the outside and probably damage any wall paper inside. It's easy to fall into the trap where you see the deflection as being say 22 mm, so you put in 25mm of say compriband.. but if you compress compriband or similar down to 3.0mm it will start to extert load on your doors.. it's good (squashy) but not that good! You also need to make sure that when the load is not there that the compriband will recover and not leave a gap. The next thing (Craig, Peter etc have touched on this I think in the past) is that there is a difference in how you install bifold doors and true sliding doors. A sliding door head can be installed with a bit of a gap over the head as they now tend to be all bottom supported, but bifold door heads need tighter packing at the head. In other words bifolds are less forgiving in terms of beam deflection. If you think about it. When the bifolds are open there is a lot of glass weight hanging out from the building so the mechanism at the head of the doors needs to be held firmly in place so that over time they still perform, the tolerances are tighter and less compatible with the structure. As promised. If you have read this far then if you have a single storey extension with a large opening you may have a flat roof above. Here you may be able to use the upstand on the flat roof to accomodate a deeper beam thus reducing any downstand in the extension. If you have a two storey house with large bifolds etc below you can start to look at turning the upper floor external wall into a big truss. This in the right circumstances can allow you almost take the doors right up to the ceiling! The secret is that there comes a point where a big steel beam is no use / economic if you have some height above to do something. If you have a modern house, say with an "L" shaped roof" and go in the attic you may see lots of thin prefabricated trusses. But at the "L" bit you may see some sturdy looking trusses.. girder trusses. You can apply the same principle to creating a large glazed opening on the ground floor. If I was looking at designing a 3.5m plus opening for glazing I would use start by saying.. I want no more than 6 - 8mm deflection at concept design stage under say snow loading or roof access. I would then look at the type of construction.. masonry, timber frame. Timber creeps over time so that has to be accounted for. I would also look to see how much the founds may settle.. if there is uneven loading.. differential settlement. Once you get a handle on the "feel" of things you are on your way to getting a problem free solution. This all may sound expensive as you need an SE, experienced designer that can look holistically at this but it may only cost a little more for the extra design input. Ideally it may end up that you save money!

What is on the outside of the solid external walls? Is this a breathable / permeable layer?

I would hang fire with the beam and block. Leave the piles and ring beam as they are. If you install the beam and block and leave it for a few years then if something starts happening in the void under (water ingress, mould etc) then you'll have to fix it.. that won't be easy and not good for moral. Also, it does limit your options. Practically you may want to run services in the solum space.. planning that far ahead? Maybe get some free draining goetextile membrane (B&Q?) and lay it over what you have. Then infill back up to ground level. Pick an inert infill material that is easy to dig out and recycle... hence the geotextile membrane. This could be a layer of recycled aggregate. Or you could just dump some broken brick, another layer of textile then some decorative aggregate, some plant pots etc so you can use the space while you wait. It may be that you have a gravel drive.. use the same aggregate so you can "top up the drive" once the work is complete. The key really is to provide a layer of material to protect the underbuilding and solum from frost. Gardeners turn over the soil before the winter to let the frost get in and break it up. Same will happen to the soil under the solum if you don't protect it from frost. The concequence will often be that you end up having to dig the material that has softend.

I learnt about ovens from my Father in law, what to look out for in terms of cleaning, the control display sizes and so on. Off topic.. Don't panic Jilly. NHBC regs touch on this, have copied below their text in italic from section 5.2 D10 of their regs. A minimum void of not less than 150mm should be provided below the underside of floor slabs and beams. On shrinkable soil where heave could take place, allowance should be made for the void to accommodate the following movements according to the shrinkage potential of the soil: high potential - 150mm medium potential - 100mm low potential - 50mm. If you get stuck then I would look to see if the ground has recovered from any trees / hedges cut down in the last two years or more.. this causes ground to swell. Also, have a look at what time of year the solum is installed, at the end of the winter where moisture contents are high and the ground has lifted/ swelled. If conditions are right you can make the point to the BCO that the ground has swelled (heaved) upwards close to it's potential maximum so once you put a dry building on top it will go down and increase the void. A reasoned argument coupled with a pragmatic BCO could resolve. This is a bit of last resort stuff to get you out a hole if you get stuck.. say main underbuilding levels set.

If you are keeping the same geometry then the oak will perform better than the soft wood. Roughly, if you think about a bit of soft wood it is made up of mainly cellulose with air gaps in the cells, it has a certain density. Oak is more dense than softer woods so you get more material and less air... thus it is "stronger". In principle the members should be fine. However, it is the connections between the timbers you need to have a look at just to make sure they are ok. If you are swapping a prefabricated softwood truss with nail plates say for an oak truss then it's worth a check on the connections. Alternatively it may be that you have a traditional cut timber roof, nailed, maybe a pole plate on the wall head. All this may need is a quantative check on the connections. In other words you can say.. the timber has a higher grade than the existing, calculate the capacity of the existing fixings and provide new fixings equal or better than the existing.