Attic Insulation - New Build

Rugger13 · 08-11-2013 03:23PM #1

Hi,

Im a newbie to these forums (and the construction game..!) so was wondering if anyone could lend me some advise regarding insulation my attic.

I am currently in the process of building my house (sub contracting - direct labour) ....I was wonder what you guys would advise me in terms of insulating my attic. What I plan to do is have 100mm Kingspan inbetween the joists...over which I plan to lay 100mm quilt insulation.

Should i go thicker than the 100mm quilt? Any other suggestions/tips would be greatly appreciated!!

Thanks

Gumbo · 08-11-2013 03:32PM

Rugger13 wrote: »

Hi,

Im a newbie to these forums (and the construction game..!) so was wondering if anyone could lend me some advise regarding insulation my attic.

I am currently in the process of building my house (sub contracting - direct labour) ....I was wonder what you guys would advise me in terms of insulating my attic. What I plan to do is have 100mm Kingspan inbetween the joists...over which I plan to lay 100mm quilt insulation.

Should i go thicker than the 100mm quilt? Any other suggestions/tips would be greatly appreciated!!

Thanks

What did your BER Agent put into his calculations/recommendation?

BryanF · 08-11-2013 03:42PM

Rugger13 wrote: »

Should i go thicker than the 100mm quilt?

Any other suggestions/tips would be greatly appreciated!!

min 300mm mineral wool or similar
you need an architect and a BER assessor ASAP

Rugger13 · 08-11-2013 04:10PM

Hi Kceire & BryanF thanks for your reply.

The plans were drawn to B1 BER...the architect suggested 200m quilt between joists and 100 quilt laid over. But Ive been advised by other builders or people ''in the know" that the 100mm Kingspan insulation boards, cut to fit between joists would be a better job (100mm then laid over that).

Should I consider a thicker Kingspan for between joists?

fclauson · 08-11-2013 04:55PM

Rugger13 wrote: »

Hi Kceire & BryanF thanks for your reply.

The plans were drawn to B1 BER...the architect suggested 200m quilt between joists and 100 quilt laid over. But Ive been advised by other builders or people ''in the know" that the 100mm Kingspan insulation boards, cut to fit between joists would be a better job (100mm then laid over that).

Should I consider a thicker Kingspan for between joists?

you will have to look at the products u-values and do the maths

Gumbo · 08-11-2013 05:21PM

Rugger13 wrote: »

Hi Kceire & BryanF thanks for your reply.

The plans were drawn to B1 BER...the architect suggested 200m quilt between joists and 100 quilt laid over. But Ive been advised by other builders or people ''in the know" that the 100mm Kingspan insulation boards, cut to fit between joists would be a better job (100mm then laid over that).

Should I consider a thicker Kingspan for between joists?

If you change the material you have to let your BER agent know so he can amend the details in the DEAP software and thus give you the new calculation.

Have you had a preliminary BER assessment carried out yet?

Rugger13 · 08-11-2013 05:26PM

Yes, I will notify him as I have upgraded my dry lining from 52.5mm to 62.5mm and a few other upgrades also. I have had the preliminary assessment yet, but hope to do so shortly.

Thanks!

MicktheMan · 08-11-2013 05:59PM

Rugger13 wrote: »

Yes, I will notify him as I have upgraded my dry lining from 52.5mm to 62.5mm and a few other upgrades also. I have had the preliminary assessment yet, but hope to do so shortly.

Thanks!

What is your exact wall build-up?

Rugger13 · 08-11-2013 06:03PM

The wall is 320mm ...120mm Cavity with 80mm Kingspan. The inside of the external walls will be plastered with a sand/cement mix for air tightness...on which the 62.5mm insulated plasterboard will be placed

MicktheMan · 08-11-2013 06:09PM

Rugger13 wrote: »

The wall is 320mm ...120mm Cavity with 80mm Kingspan. The inside of the external walls will be plastered with a sand/cement mix for air tightness...on which the 62.5mm insulated plasterboard will be placed

Good that you have included your air tight layer.
I'd be a bit concerned about where the dew point of the wall will be though.

Rugger13 · 08-11-2013 06:19PM

Thanks for your reply Mick.

Hmmmm....I guess its something I haven't thought about...I thought by trying to go with a good thick drylining board it would be beneficial..do you think it will cause mould etc in the room? Would there be anyway to counteract this happening? As I say...im a total newbie to all this...just took a punt on the direct labour route to save on the contractor fee's! (The insulated plasterboard is foiled back..would that help with the dew point..sorry if this is a stupid question!)

MicktheMan · 08-11-2013 06:32PM

Rugger13 wrote: »

1. I thought by trying to go with a good thick drylining board it would be beneficial..
2. do you think it will cause mould etc in the room?
3. Would there be anyway to counteract this happening?
4. As I say...im a total newbie to all this...just took a punt on the direct labour route to save on the contractor fee's!
5. (The insulated plasterboard is foiled back..would that help with the dew point..sorry if this is a stupid question!)

1. Ideally, insulation should be in one place.
2. There is a definite risk of interstitial condensation happening at the back of the board which mould will love
3. The general rule of thumb is that the internal insulation effectiveness should be less than half that of the external. Also, internal moisture load, heating regime and ventilation will vary the risk.
4. Then get professional independent advise (i.e. not from dave down the pub, salesmen etc)
5. No

Rugger13 · 08-11-2013 06:49PM

Thanks Mick

john_cappa · 08-11-2013 07:15PM

Off the top of my head my attic spec is 150 mm laid between joists, 300 mm on top. Standard enough loft roll.

Rugger13 · 08-11-2013 07:16PM

Thanks John!

jamesf25 · 13-11-2013 09:17PM

Spray foam rafters in attic u will eliminate all draughts also it will be a heated store for wat ever. Stuffing in quilt insulation isn't an exact science ! Very tough to do extra few quid spray foam and attic is air tight.

Rugger13 · 13-11-2013 09:24PM

Thanks James. I'd say the spray foam
Would have been a great job but I'd ordered the materials Im using now. Approach I'm going with:

- 32.5mm insulated plasterboard (ceiling)
- 100mm kingspan boards cut to fit tightly between joists (this is being done at present)
- 100mm earth wool on top of kingspan
- 200mm earth wool runnin in the opposite direction on top of kingspan & 100mm earth wool

fclauson · 13-11-2013 09:28PM

jamesf25 wrote: »

Spray foam rafters in attic u will eliminate all draughts also it will be a heated store for wat ever. Stuffing in quilt insulation isn't an exact science ! Very tough to do extra few quid spray foam and attic is air tight.

Make sure IAB is followed in terms of ventilation
and moisture control

fclauson · 13-11-2013 09:29PM

Rugger13 wrote: »

Thanks James. I'd say the spray foam
Would have been a great job but I'd ordered the materials Im using now. Approach I'm going with:

- 32.5mm insulated plasterboard (ceiling)
- 100mm kingspan boards cut to fit tightly between joists (this is being done at present)
- 100mm earth wool on top of kingspan
- 200mm earth wool runnin in the opposite direction on top of kingspan & 100mm earth wool

Make sure you get the eves right - you have ensured that the ceiling is warm so it's the ceiling to wall junctions which could be colder if not done right

Rugger13 · 13-11-2013 09:31PM

fclauson wrote: »

Make sure you get the eves right - you have ensured that the ceiling is warm so it's the ceiling to wall junctions which could be colder if not done right

Will do, thanks!

Attic Insulation - New Build

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