saveasteading

So this is for ease of construction. Let me paraphrase to check my understanding. Fix bottom plate to foundation masonry. Make a section of wall on the ground, including top and bottom timbers (as if in a factory though this is to be stick-built) and lift panel into place. Nail down and prop in place. When enough panels in place fix continuous header over the top of them all. Hence 13mm osb reduces the weight for the heave into place. Strength of wall increased by extra timber top and bottom. The timber price this way has gone up by £150, but the OSB down by £300 (cf 18mm) and the joiner will surely be very happy, so reduce his quote (or not increase it.) and do you think 13mm on the roof too? I can't see osb3 at 13mm. 11 or 12 depending on source. What size of panel is normal, assuming 2 workers, or if 3?

Agreed with Iceverge. OR you need a decent slope and also an utterly watertight seal of metal to roof, using mastic and lots of screws (which you should anyway. I would lap the roofing over the edge so that any stray dribbles go outside your wall cladding. Even better would be to dress the roof covering up a batten that forms an edge. the metal trim is best not being 2 flats faces like that, as that will distort when screwed. better to have it shaped like my dodgy sketch attached. the 180 returns are 'welts' and stiffen considerably, as do the other bends. That will look much stsraighter and allow much tighter (and more watertight) fixing, with a bead of special mastic underneath. That will cost twice what a 90 deg one will, so is up to you.

Beautiful if it works, but very risky. All concrete cracks. If poured to perfection the cracks will be invisible but will still be there, to collect dust, and to show up whenever there is a spill. so it needs a lacquer finish. Look closely at the floor in a b&q for example and there are cracks everywhere. If you mean a ground, polished finish, with the stones visible then the same applies. The cracks will be severe if you don't create a box-out around the columns to let it move as the concrete shrinks. I recommend separating the functional concrete floor from the finished screed in a domestic situation. They cannot float it to kitchen specifications. The workers pouring your slab are not thinking about an internal finish. And what if it is raining? You can later screed in many finishes, including very expensive, polished, exposed aggregate.

1. Recommendations for OSB thicknesses please. I have designed a section of rebuild in timber, using the Scottish document for it. For the sheathing of the walls and roof they require minimum 9mm OSB class3. That doesn't seem a lot for what is holding up the building. But the cost saving compared to say 18mm is significant. (if I can save 25% on every element of construction, then it becomes 25% of a lot.) What do the experienced roofers and Engineers (and clients) among you think? Easy to say 18mm when specifying and someone else is paying. Walls are 140 x 50 stud, timber clad. Roof raised tie trusses 220 x 50 rafters, and a metal clad surface. (The design guide assumes concrete tiles) 2. Between you , in other posts, you have recommended using double stud at foot and head of the new timber walls. The design guide doesn't mention that as a necessity. In most sketches it shows single and in one sketch it shows double. If the roof trusses align with the wall struts, I cant see why double helps. It does of course stiffen the whole building and provide a substantial longitudinal tie, but that should not be necessary. And there will be treble C24 timbers at lintels, which will pick up intermediate trusses. Comments on the practicalities as well as design theory will be welcomed.

All I can add, in case it helps, is that we put air-source to air-ducted space heating into our big office. A USA system. The internal circulation was simply a plenum box with a 'hot' radiator in it over which the air was forced. The distribution pipes were about 100 dia then splitting into 50mm tendrils. I think the principle was that all the ducting was much the same length to keep all the flows the same. Worked fine, and when the outdoor temperature was silly low (v cold winters sometimes in SE England) and the four ashp units were struggling, an electric heater kicked in at the plenum. Much easier in an open plan with a single recovery duct than with multiple rooms, I think.

And yet, such slabs are usually specified only for large spans or heavy loads. I can't think I ever specified them for other than that as they need to be craned. Also note that there is almost certainly a crown, so there will be much ticker screed at the ends

So the screed is 'OK' at 30mm but what does the plank need to perform as specified? The screed on a hollow-core floor is an important part of the strength, unless yours has been specified conservatively. Check.

20 miles from Inverness, but the other side of the Firth.. 1880 farm steading. Proximity doesn't matter, but dealing with similar processes, and to satisfy the same council, does. Happy to help if I can.

Thanks Gordo How interesting. A very different approach. My dislike of insulated plasterboard is the cost. That is near to £50/sheet which is an expensive way to buy polystyrene. 50 x 50 would certainly be a lot cheaper, but the timbers are seldom straight and I would be concerned about alignment, even with a fixing strap, which I don't fancy screwing into granite too often. May consider for shorter heights.. (I have had 50x50 which had a 90 degree rotation in the length, as supplied.) Does 100mm dritherm hold between 50mm studs? It is half the price of PIR but half the insulation, so an interesting balance. Needs a vapour barrier behind the studs, which will clash with the dritherm, and an airtight barrier on the room side. 25mm gap yes. Do you mean intumescent to stop ventilation in case of fire, rather than 'allow'? Anyway there is only the polystyrene to burn, as wood seldom does without a lot of heat, so I don't see this as necessary There are targets for insulation in conversions, but not regulations. Conversion of Traditional Buildings Whilst achieving the U-values recommended in clause 6.2.6 and 6.2.7 should remain the aim, a flexible approach to improvement should be taken, based upon investigation of the traditional construction, form and character of the building and ......other than where proposed works are wholly categorised as a conversion, where the standard in question may be met as far as is reasonably practicable However we are aiming for something better than the recommendations, hence the juggling. I do appreciate your comments, but need further convincing.

I think your idea of ventilated is very different to what the timber industry do. I worked on a few buildings for them and the amount of ventilation is huge. They want a constant draught through the shed. Plywood is particularly vulnerable as the layers are cut from a log as with a pencil sharpener. The surface therefore has the rings spread out and the softer wood is more porous and vulnerable. You can see this on the photos as rings and repeated knots. Seal the wood or create a lot of air movement say I.

My habit is to do holistic designs, ie everything considered before we even submit for Building Warrant/ Regulations. The alternative is a linear process where everything is made to work with what was before it. Hence I am hoping not to have any regrets about previous decisions, and to keep the cost to our demanding budget. The cost difference for the same quality can be huge, from experience. Even worse if it is out of close control. Hence the original question. Yes we can change our minds, and tweak as we go, but I would rather not. Re Gus's points. We are lucky with the ground. Or rather, we knew what the ground was before committing to the purchase. It is pure sand, other than some cobbles, probably for 10m. Research shows that this was dropped by glaciers, some time ago, hence the sand is single sized, as are the cobbles, and the drainage is excellent. Heating. underfloor, from Air Source unless anything changes soon. Have discounted boreholes as they are expensive to install and can go wrong. Could still be persuaded to go with slinky in the ground, as the ground is easy to dig, and there is enough land. This is not ground source really as the heat comes from the sun and air, and is seasonal, as is ASHP. Composite would be good but probably too complex. Insulation: if we put lots in the walls, the rooms become too narrow. Lots in the roof, and some head-rooms become too low. Lots in the floor and we bump heads on existing lintels. Dig out the floor and risk disturbing the shallow footings......and the floors are at varying levels anyway......and so we juggle all of these. A section of the building has moved....consequently the rafters have rotten ends, and the walls are in a poor state. I wanted to hoist and repair with splicing but am over-ruled but, fundamentally, no local joiners were interested anyway. So we will remove that bit (20%) and rebuild all in timber. When built nobody will know the difference. This is all so much more difficult than new build.

150 rafters, with 20mm ventilated sarking then slates. There is no prescribed U value as it is a conversion. 'As good as reasonably practicable' which includes cost. Aiming for new-build standards where possible then will use pragmatism. Can't offset it all in walls or roof due to the geometry (narrow and sometimes low)

If it was the fee would be very much higher. Some good BCOs are very busy dealing with problem jobs, and the deliberate cutting of quality, and so see the rest of us less often. I give them the benefit of the doubt, and don't expect them to know everything. They are allowed to be mistaken, but I would expect them to back down when necessary.

I hadn't thought of the sarking as a top flange to the roof trusses. Probably because we do have some outward leaning walls. This is now a clincher in choosing to use OSB rather than traditional 200 wide timber boards with the 2mm ventilation gap, wherever we have to rebuild. The 2mm gaps are enough to allow the rafter to bend upward and outward and to lose the flange benefit. From my current homework, the guidance for a new timber structure is to have a structural pod of a controlled area, and to further stiffen by building cross walls as stiffening. It is not there to stop the roof from splaying, but it will. For normal sized rooms this is straight forward but requires more foundations and OSB on the partition walls. The same logic will apply with masonry walls. JackOfAll....do you have normal or big rooms?

This is now available in any Google search. I hope your alias is obscure enough. But you are right on the rest. I had the misfortune to manage an underpinning process many years ago, The company had tendered and won it, never having done it before. Doing it properly was much slower than they had estimated. My boss, who knew very little, insisted it went much faster, affecting the amount undermined and the shrinking /packing process, and I moved on to a better place. I am sure the same still happens. The building inspector does not inspect often, or in close detail at all. If I was an insurer I would not be interested. Mr Punter is probably right though...there is no current problem (only a concern) so it is simply covered by your normal building insurance, who would then sue the builder and Engineer if there was ever a problem.

Batt insulation is half the insulation performance and isn't enough Sprayfoam, no never. blown in....polystyrene balls or newspaper....no thanks. One chance to get this right.

All very good info and a brilliant document I had not seen, thanks. From a very quick look.....and some guessing. Impervious granite with small percentage of mortar on the faces, (therefore dry ), huge percentage of mortar in the middle which, as you say, has a decent thermal resistance. I will have a detailed read.

I agree re the labour on the timber, and another element of wood to add back in to the equation, but perhaps a detail will present itself. On the other hand, cutting PIR into the voids is also a horrible job, and that labour is reduced too. I didn't mention that the rafters are very approximately 18" c/c. Can be anywhere from 380 to 420 gaps. I thought these old builders were more precise than that. Perhaps with 600cc the c/c will average out. Every piece of PIR in the roof will have to be measured.....grrrrrr. As posted elsewhere, we have rerun this wall liner with 100mm studs and it is good for insulation, so that will save us a lot of timber. Also I have found that standard CLS (or near) can be much cheaper if bought by complete pallet, effectively straight from the docks with no handling by the merchant. I'd like to use local timber, but the mills say that Russian/Finnish will be cheaper for CLS. I'm not so sure. published local price for C16 treated is 100mm x 50mm x 3.6m £9.18 Excluding VAT that is per one, collected, so there will be discounts. We will 100 x 50 (or 38) at 600cc and reconsider later, especially for the longer sections. Then if we revert to 400cc there will be no prob from the BCO.

There is every reason to assume that your own work will be diligent and thorough, and possibly better than some contractors. They don't always put their best people on gutty work like this. But I'm not confident an insurer will be excited about the business as a one-off. If one Engineer says it doesn't need it, then it does seem completely precautionary by the other, or a marginal decision. Which one seems the more specialist and experienced in such works?

Have done further consideration and re-analysed the U value. we are now 600 granite (in 3 skins) 25 air gap VB 100 stud with PIR VCL 25 air gap and horiz studs pbd. U value is about 0.15. a lot of this is because the 25mm air gaps give better values than if filled with rockwool unlikely I know, but narrow gaps do work quite well. Also Granite is highly rated by heritage building authorities, as providing 'much better insulation than the regulations and standards assume'. I think this is because of the random 3 layer construction, and that there is relatively little mortar in the faces. As we don't have to match any standards in a conversion, we are happy to believe what we have come up with. Also, the reality of the stone walls is that there is hardly any dampness on the surface, for the wind to evaporate and suck out heat. granite 2.6tonnes /m3 and stones averaging 300 x 300 There certainly wont be summer overheating through the walls. The Standard states Wall studs to internal racking walls should be at least 38 x 89 size, grade C16 at 600 mm centres. and there does not appear to be any situation that reruires more.

Ok I a am a cynic. But whenever I have had a recommendation from a specialist, for methane usually, they have allowed complex ventilation underneath as well as seals, and all to be carried out by a specialist installer. So I looked into this is a big way, as I had several jobs on or near landfill. Since then we did it ourselves at about 1/4 the cost. It still needed physical ventilation beyond a certain distance from the outside walls, and in one case (because of distances,) a constant fan. The difference in cost, apart from margins, was that plastic pipes came without 'methane pipes by the acme safety company' written on them. ditto the membrane, So by all means get it designed by a specialist, but I suggest diy, or by the builder with close attention to quality. Ventilation or not will depend on the distance to the perimeter, ie size of building. It is an a fairly accessible document. Perforated pipes under the building, or ventilate the void, as applicable, with the barrier in place and sealed everywhere. The gas just wants to escape so make it easy

I see what you mean. Specify as in 'state that it is a design requirement', or specify as in 'choose a manufacturer? AS I understand it, it is simply a dpm where the plastic is right chemically and in thickness that gas with radon in it can't get through. It used to come from very specialist suppliers with 'danger radon beneath here' written all over it in red on yellow. Now it comes from toolstation for £0.70/m2.

Sorry. sounds like an obscure specification. I meant that it wasn't new (and not anew problem) , perhaps very old.

Thanks. That is what I would expect and want, but it didn't look that much.; The design guide accepts down to 38 x 89 @ 600cc which seems tiny. I haven't looked at how small the building and benign the conditions for that.

Whoever is presenting the design. Architect, Engineer, yourself. Simply look up the definitive website and pay for the information. About £3 if I recall. Answer emailed in a few seconds and you simply include that page in your submission. The extra cost of a radon rated dpc isn't as bad as it used to be. http://mapapps2.bgs.ac.uk/geoindex/home.html?layer=BGSRadon&_ga=2.106057667.1323565302.1635198583-1743045500.1633718990