saveasteading

OK. I have seen heave once. I think clay heave is assumed too often but I don't know your ground conditions. Clay heaves when it was dry and gets wet. If the whole area is rising and falling then it doesn't matter. Under a 15x9 slab will it be much drier or wetter than the surroundings? If you had conventional footings at 1m deep then they won't budge, and the slab will be on fairly standard ground. OR refer to another discussion on here about beam and block. No heave.

I posted this in error in another discussion on the same subject. and have mixed the 2 up I think. No time to review so here it is again. My thoughts. questions first. Where is the floor insulation? Is the ground levelish and good bearing capacity? Assuming the ground is good, I would lay harcore and 150mm slab. 175 maybe . Crack control mesh is all that is needed. This suffices in warehouses and commercial vehicle garages so is ok for your sofa. Lay PIR on that with ufh on top, then screed in 60mm poured or hand laid. If you need more capacity for internal loadbearing walls then it can either have a thickening in the slab, or a trench footing, as the ground dictates. I think rafts are specified too often. I really don't like structural slabs on top of insulation. Now some other points. 85m3 isn't much and I will stab at it being about 8m x 10m. I'd have to check but this is close to not needing any contraction joints for a finished surface. But with a screed over it that is irrelevant because the slab will crack well before the rest of the work, and will not reflect through the screed. Even as a finished surface this cracking would be trivial. With careful mix control (absolutely don't allow extra water added on site) and fibre additive (£30 or so) any cracking will be microscopic. Cracks would be tiny and many. The UFH pipes will likely debond at cracks but are also well capable of stretching the 1/10th mm required. I did put UFH into a 175mm slab once, as the client's specific requirement. (It was a factory and this was the area where people stood to do craftmanship stuff.) It had anti-crack mesh in the floor, and the UFH pipes were fixed on top of it. Shrinkage joints were either the old fashioned method of pouring alternate long strips, or crack inducers built in....I can't remember. So there was no cutting into the slab afterwards. More mesh reduces crack width if necessary, which it wasn't in this case. I guess the shrinkage cracks were about 1mm. It went well and worked welI. I heard no more about it so it must have been ok. I had a further job for them so it's not as if we lost touch either. It was an uninsulated for various reasons I won't divert into. btw I've done 200,000 m2 of slabs and never more than 175mm when ground bearing. So there are choices. Even the best SEs don't know all the ins and outs of costings (it isn't just the slab but the walls, the insulation , UFH , access to site)......That needs a close collaboration between contractors and consultants. The biggest and best contractors will know, if they have an SE inhouse, or have developed a standard method. But that will cost you in either overheads or conservative design. Small contractors may well know, but that is rare, and with some, the less they know, the more they think they know. BUT perhaps they and your SE together can optimise this. If there is a reason against my suggested method, then please say.

I may have mixed up 2 current discussions! take what is relevant.

My thoughts. questions first. Where is the floor insulation? Is the ground levelish and good bearing capacity? Assuming the ground is good, I would lay harcore and 150mm slab. 175 maybe . Crack control mesh is all that is needed. This suffices in warehouses and commercial vehicle garages so is ok for your sofa. Lay PIR on that with ufh on top, then screed in 60mm poured or hand laid. If you need more capacity for internal loadbearing walls then it can either have a thickening in the slab, or a trench footing, as the ground dictates. I think rafts are specified too often. I really don't like structural slabs on top of insulation. Now some other points. 85m3 isn't much and I will stab at it being about 8m x 10m. I'd have to check but this is close to not needing any contraction joints for a finished surface. But with a screed over it that is irrelevant because the slab will crack well before the rest of the work, and will not reflect through the screed. Even as a finished surface this cracking would be trivial. With careful mix control (absolutely don't allow extra water added on site) and fibre additive (£30 or so) any cracking will be microscopic. Cracks would be tiny and many. The UFH pipes will likely debond at cracks but are also well capable of stretching the 1/10th mm required. I did put UFH into a 175mm slab once, as the client's specific requirement. (It was a factory and this was the area where people stood to do craftmanship stuff.) It had anti-crack mesh in the floor, and the UFH pipes were fixed on top of it. Shrinkage joints were either the old fashioned method of pouring alternate long strips, or crack inducers built in....I can't remember. So there was no cutting into the slab afterwards. More mesh reduces crack width if necessary, which it wasn't in this case. I guess the shrinkage cracks were about 1mm. It went well and worked welI. I heard no more about it so it must have been ok. I had a further job for them so it's not as if we lost touch either. It was an uninsulated for various reasons I won't divert into. btw I've done 200,000 m2 of slabs and never more than 175mm when ground bearing. So there are choices. Even the best SEs don't know all the ins and outs of costings (it isn't just the slab but the walls, the insulation , UFH , access to site)......That needs a close collaboration between contractors and consultants. The biggest and best contractors will know, if they have an SE inhouse, or have developed a standard method. But that will cost you in either overheads or conservative design. Small contractors may well know, but that is rare, and with some, the less they know, the more they think they know. BUT perhaps they and your SE together can optimise this. If there is a reason against my suggested method, then please say.

Everybody is right here....my pennyworth tomorrow.

Deflection is shown on the design tables so is predictable. In reality I've never felt a b&b floor bounce even in the raw state. A screed is often part of the design. Even adding a grout brushed into the joints makes an improvement.

Pir between joists I favour half pir and half mineral wool. The thinner pir can be cut more accurately and the wool is squeezed in and completes the seal. Doesn't expanding foam shrink too?

OK to summarise my thoughts. I have often used, and would again use, B and B. This has been as the ground floor on sports halls where the ground sloped and a ground bearing slab was not my preference. It jumps gaps between sleeper walls, is as solid as we choose to specify it (no bounce), and won't rot. In one case, the access to a big hall was so awful that b&b allowed for manual handling if the worst of the winter prevented lorries from getting near. The floors are strong and hard enough even before screeding to support cherry pickers...with great care. Timber will not allow that. Also used on the first floor on office blocks and classrooms and similar areas. These are big spans and the loading is quite high, and timber would have been rather deep. But it is becoming a close thing between b and b , or steel joists, or timber I joists. Plus there is the density for sound absorption, especially if there are different occupiers and they shouldn't be aware of the neighbours. For a house I would always consider b&b, but would compare it to the other options. Even the house dimensions or room arrangement could swing the decision.

Show it to your builder perhaps. Some of these guys are strong and don't mind the weather....and that is about it for suitability. Maybe with knowledge he will improve.

No problem, but please introduce future queries with that proviso. it stops us going into panic 'don't do it' mode, which some queries need.

As @Nickfromwalessays. A block in beam and block can crack but not budge, and nobody knows ad nothing happens. BUT you wouldn't want a heavy, especially loadbearing, wall on it Timber stud floor plates will spread the load. masonry walls would best have some reinforcement . BUT most of all, has the floor as a whole got the capacity for this extra load?

Including the measurement, collection and the risk. I've just checked. The 1000 x 800 one we got last year was £140 incl vat, collected from the company 200m away. I paid that direct. Fitter charged £75. Yours is 50% bigger. Price thus seems fine.

Good point. They will still 'breathe' though.

I'm of the opinion that this is a good, though expensive, way of reducing heat loss yet keeping ventilation. Ignoring fire lit times, Outdoor air flows up the chimney and keeps it dry. Perhaps that reverses sometimes. Indoor, heated air cannot rush up and out. It is shocking how much warm air is flying out of our chimney without a fire lit. I had one of those umbrella thingies in our open fire but lost it...you know how. That would have been even messier with a bin bag of fibreglass, which I may stuff up. Payback about 10 minutes. Risk??

There is usually reclaimed timber on Marketplace, but barely cheaper than new. Perhaps it sells to people who just assume it's a bargain.

All good advice. Where does surface water go? Towards this wall or away from it? Keep your gravel lower than the drive so that it can hold water until it soaks away. The gravel will need cleaning every year or so but this is easy.

Presumably all natural forests have changed genetically to suit the circumstances. Then they replant as monoculture with something faster growing and alien. Commercial forests are not generally attractive to be in for human leisure, and are deserts of needles and darkness on the ground. But I still favour timber. We must wish @Pendiclewell in reusing the salvaged timber. I think I can tell C24 from C16 by sight. Especially as C24 appears to be more wide grained than in the past.

It is because the trees grow very quickly in the climate, unlike cold places where the growth rings are closer together ( eg Finland, Canada, and previously Russia). Also i was informed by a Finnish timber merchant manager that their flat land results in straightness and strength.

Sorry, you're right of course, I'm mixing up who's project we are looking at, re zero or 5% then explaining badly. This is right though isn't it. The 20% tax back on materials bought direct does apply but it can be quite a cash investment, IF it saves money at the time, then waiting a long time for it back. Saving will depend on the builder's account levels, and on how they value risk or margin on materials. I had one job where the contractor was taking some of our plasterboard every night...that's another matter though.

If Only. They invoice at 5% VAT but you can reclaim it at the end of the job, so must keep very detailed records. Materials you an buy yourself, pay 20% and also reclaim. Equipment used for construction, you can't claim back Be sure that your work complies with the requirements. Renovation does not and is all 20%. New build or conversion does, as above. And you still have to allow for the cashflow, as it will be out of your hands a long time.

Good point. A UK Power guy dated a pole to the late 1940s based on having a wide grain and lots of knots...ie a British fir tree that grew rapidly, and was all there was. Even now you can buy Highlands timber that is C16 or ungraded, but not C24.

That seems an awful lot, after a leaf filter. My 1920s brick single chamber cess tank had that much on the bottom. Not bits of leaves. Any idea what it is? would you change anything another time?

Great idea to reuse it. Its quite likely better than at the local BM anyway. Photos of it? Most timber is visually graded, from the closeness of rhe growth rings and the amount of knots. So you need help from your BM (agree to buy everything else from them) or an SE. OR you could design as if it as C16 timber and be on the safe side.

This last year has had very little input from me, but masses of work by daughter and soninlaw. They have excelled. They've been boarding in the stairway today too. A shame to lose the storage space but needs must.

got a name ? Anything good or annoying about it? eg bright display or sounds.