timber frame wall thickness/insulation

[valmet10]

hi not sure if I ask in here or in the insulation page sorry if I'm wrong

I'm not sure but is there a minimum thickness of outside wall to meet building regs for insulation on a single story house built using timber frame /sip's

not sure need to use cheapest /value for money

 

[Crofter]

Hi and welcome to the forum.

The building regulations don't specify a wall thickness per se, but they do require a certain insulation value (U Value). Different materials have better or worse insulating properties so the eventual thickness depends on what you use.

 

Normally you would set a target U value and then work to that. Just to throw out a very rough number, I think you will find that you would need 150-200mm of insulation to get a low enough U value. Then you have your plasterboard etc on the inside, and whatever your finish is on the exterior.

 

You will find a lot of people (especially on this forum anyway) will tend to specify more insulation than the building regs minimum. In my own house, I have aimed to put my money into the building fabric and then spend less on the heating system. This can be a good tradeoff as insulation is a one-off cost, unlike running your heating.

 

Is your wall thickness constrained by budget or space?

[ProDave]

The "normal" timber framed house in these parts has a 150mm frame filled with insulation and quite likely a thin layer of something else inside.

An important question is what is going on the outside?

The traditional timber framed houses up here have a brick or block outer skin, but because the cavity has to be ventilated, the outer skin adds very little to the insulation, and is just an expensive rain screen.  So as well as having a thicker than normal timber frame, I have chosen to clad mine in 100mm thick wood fibre external wall insulation and the render is applied directly to that.  As a very rough ball park figure, the external wall insulation system is a similar cost to a blockwork skin, but helps to make the building more airtight, and adds more insulation.

[valmet10]

the outside skin is going to be box profile steel sheet

has for "Is your wall thickness constrained by budget or space"

at the minute it's budget  but as a farmer , I want the best for the least , not really sure what best to use is the any website that shows value /to cost per sq metre

[Crofter]

I see from your other posts that this is a barn conversion. I presume it's a steel portal frame in which case you are not looking to build a structure, rather just an insulating lining. In that case, I would probably steer away from SIPs as they are not the cheap option.

The best insulation per £ is rock or mineral wool. That's why it's used in lofts, where it can be as deep as you like.

If you need your insulation to take up less space, you can use polystyrene, or Kingspan/Celotex- but these will ultimately cost more. It's also harder to get the rigid insulation to fit tightly, and if it isn't tight then it won't do its job.

 

If you are constrained by budget then it is possible to design cheap, without too many compromises. Things that add cost include chimneys, too many windows (especially multiple small windows), and odd shaped buildings- these things all lose heat as well, so it's a win win if you design them out.

[valmet10]

It's a timber framed barn basically wanting to build a timber insulated box inside an existing barn , minimal windows, one bed room /shower room. Everything else open plan, one wood burner in middle of house.

Was not sure best way to build box look at SIPs for ease of build, but cost does come in to it , or use 6x2 and osb board we have a full joiners shop at the farm so pre fab wouldn't be a problem

 

[Crofter]

I expect SIPs will be much more costly than building your own stick/board frame. Plus it sounds like a pain getting big prefab panels into the barn.

 

Sounds totally viable, though. What are your thoughts for the floor?

[valmet10]

been looking at using easi joist or similar sat on rsj's sat on concrete pillars going to insulate between  joists and chipboard flooring

[ProDave]

Originally my timber frame was going to be filled with one of the blown in types of insulation. However when I loked at costings i found that was an expensive option.

So I have chosen to fill my frame with Knauf Earthwool frametherm 35 which is under half the cost of the blown in stuff and gives the same U value.  I have 190mm of that in the frame plus my 100mm EWI.

I would consider something similar. I spent £1200 on insulation and that is more than enough to do all my walls (what is left over will be used under the floor or in the roof) so you don't have to pay huge amounts.  I would also look at over sheeting on the inside with one of the PUR type insulations sheets, e.g kingspan, celotex etc to mitigatecold bridging of the frame members.

[Crofter]

5 minutes ago, valmet10 said:

been looking at using easi joist or similar sat on rsj's sat on concrete pillars going to insulate between  joists and chipboard flooring

Is it just bare earth at the moment?

[valmet10]

hardcore / earth with a bad slope and a step  that's why I was thinking along above lines plus I have the rsj's

[Crofter]

Ah OK that would make sense to deal with the slope I guess. Engineered joists are nice things to work with- I used JJI joists on my own build, very easy to handle and they don't bow like solid timber does.

The other option would have been a slab, i.e. dig down to firm ground, lay and whack down some sub base, EPS insulation layer, and then a concrete screed on the top. But if the site is sloping that could make for a lot of work.