Concrete floors and insulation

My barn rebuild is approaching the point where I need to decide the order of laying the floor.

Ultimate finished floor level can be determined by allowing 6'6" below the bottom of the beams. However, advice in here, constructional guidance in books (oldish) and what our builders did varies.

Eg. in 1995 the builders method was compacted hard-core, dpm, 4" over site concrete, 2" polystyrene sheet and 2" floor screed.

My Collins DIY manual has compacted hard-core, dpm, insulation taped at joins (with what?) concrete and then screed.

I plan to use the building as a workshop initially and am concerned that shunting bits of heavy machinery around might damage a floor laid on insulation. Also, leaving the insulation to the future gives better options such as underfloor heating. Reducing thermal mass must be useful for rapid warm up but is there anything else to consider. Do building regs. specify a thickness of underfloor insulation, is this fixed or is this part of an overall calculation? Does insulation come in different load bearing qualities?

Once I know how the floor goes I can sort out damp course levels for the wall.

regards

Reply to
Tim Lamb
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Your post isn't very clear. Do you have planning permission? Do you have plans? - if so what do the plans say?

Normal procedure is as per your collins manual: hardcore (if required), followed by a sheet of DPM (usually on a thin bed of sand to prevent puncture by the hardcore), followed by insulation (this has recently doubled in thickness from 50mm to 100mm, but i assume this could be regional) followed by concrete and screed last. You are correct in thinking that the polystyrene (or whatever) shouldn't be under the screed. The taping of the joints is not really important and I've never known a BC officer to push it, providing there are no large gaps that the concrete can go down between sheets, an easy way around this is to have strips of polystrene (4 by 1 inch) to 'wedge' around the edges which will close any gaps in the middle.

If you plan on converting it to living quarters later on you'd be wise to get it done properly now, meaning you need 4' of insulation

Reply to
Phil L

In message , Phil L writes

Sorry. I should have said this is a partial rebuild of a Victorian agricultural building. No plans but I am trying to comply with Building regs. for future proofing:-)

OK

Works OK though. We have a quarry tile floor under Synthaproof seal 50 mm of insulation and 50mm screed.

Fitted carpet though so who knows what is going on under the bookcase:-)

You are supposed to bring the insulation up round the concrete to avoid cold bridging.

This is metropolitan greenbelt so unlikely however, office/B&B possible.

I hope that is 4" BTW.

regards

Reply to
Tim Lamb

Have a look at Kingspan's site (they make insulation):

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of useful downloadable pdf files showing different configurations of floors.

David

Reply to
Lobster

Should be ideally 2 metres which is 6'6 and three quarters of an inch. Sorry to be pedantic but you don't want to be up against a jobs worth building inspector.

?

If space is a premiun then the ideal make up would be min 100mm hardcore 60 mm celotex or kingspan insulation( you might need more dependant on the perimeter to area of floor), d.p.m and 100mm trowel finished concrete.

Legin

Reply to
legin

In message , legin writes

OK. I thought this had been relaxed recently? The only concern is that more head room equates to being closer to the flood level from the nearby river.

Ah. Please explain. As an old milking shed this is a very linear building: around 13m long and 5m wide. Why trowel finish?

regards

Reply to
Tim Lamb

In message , Lobster writes

Been there. Bit of a pain on dial up. Ta.

regards

Reply to
Tim Lamb

I guess so that you don't have to put anything on top to smooth it..

Reply to
Chris Bacon

Ah, dial-up.... eew. Nevertheless, there's a number to ring whereby they'll send you out any of the booklets you want by snailmail.

David

Reply to
Lobster

I assumed that this was to reduce the overall thickness. You would normally have rough concrete covered by smooth screed. If you trowel finish the concrete, you have smooth concrete instead and remove the need for 2" of screed.

Reply to
Roger Mills

In message , Roger Mills writes

My vague plan was to lay concrete for the workshop floor: finished some

100mm or so below damp course such that I could install insulation and possibly underfloor heating at a later date. Putting the insulation under the main slab has rather thrown me:-)

Screed is rather different to concrete in that it will take a nail.

regards

Reply to
Tim Lamb

Concrete will take a nail when backed up by a .22 cartridge in a Hilti gun...;-)

Reply to
The Natural Philosopher

not much use if it has got underfloor heating pipes in it though? Put down the hardcore, insulate, lay in some reinforced mesh, put in your ufh coils strapped to the mesh at 200mm centres ( the last mesh I used was spaced at 200 anyway so made it a doddle). Ensure the coils are a maximum length of 100 metres or you will burn pumps out and restrict heat. Pour in the concrete, level and trowel up. Then make sure you don't start driving nails into it. You can always glue down timber for partitions or whatever.

Regards Legin

Reply to
legin

In message , legin writes

Umm. Heating was intended to be a future option subject to successful planning for a change of use.

Please sir Mr. Planner, I have this agricultural building insulated to BR and ready fitted with domestic rated underfloor heating! It may not be a reason for refusal but it certainly sticks my neck out financially:-(

According to Kingspan, I can superimpose insulation and screed on top of an existing concrete floor. This seems the most flexible solution. It lowers the thermal mass (which may be a requirement by the time I get round to it). They suggest 75mm screed for other than domestic use. I now understand the point about floor area/circumference ratio affecting flooring heat loss. The illustration shows a much thinner section of insulation preventing cold bridging; presumably for constructional reasons?

regards

Reply to
Tim Lamb

Oh..you forgot. PRESURRISE THE PIPES FIRST to prevent crushing and loss of flow.

Reply to
The Natural Philosopher

Actually, adding pipework ALONE and insulation to a new build concrete floor is surprisingly cheap. My costs for this were little different from insulating and adding enough radiators and pipes..indeed with coper at record prices, probably less. Its the manifolds, pumps relays and temp reducing valves that make it more expensive.

Thats what I have. Poly not kingspan though.

Cold bridging is by definition over a small area, and need not be insulated as effectively as a large surface..

Reply to
The Natural Philosopher

In message , The Natural Philosopher writes

I have mentioned before the opportunity to go for a *green scheme* with water from the river upgraded via a heat pump. ISTR AJH pointing out that temperatures are low compared with conventional boiler outputs. The discussion at the time centred on ducted warm air which I happen to dislike. I am rather hoping that it might suit under floor pipework.

In any event, this is years away. My concern at the moment is to make sure that insulation and screed can be fitted later leaving sufficient headroom.

regards

Reply to
Tim Lamb

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