PIR + soundproofing over the top?

[BerryNewbie]

Hi guys,

I’m building my own garden room for all year round purpose. I wanted the insulate with PIR and add soundproofing on top. But I’m actually starting to doubt whether I need PIR at all! Without the PIR, the wall layers would be (from outside in):
- 40 mm tongue and groove timber
- 2 layers of r14 (3,5 inch) fibreglass
- one or two layers of 15mm acoustic plaster board.

Do you reckon I might as well leave out the PIR? It’s meant to be an office all year round!

Thanks!

 

[noseall]

Hi guys,

I’m building my own garden room for all year round purpose. I wanted the insulate with PIR and add soundproofing on top. But I’m actually starting to doubt whether I need PIR at all! Without the PIR, the wall layers would be (from outside in):
- 40 mm tongue and groove timber
- 2 layers of r14 (3,5 inch) fibreglass
- one or two layers of 15mm acoustic plaster board.

Do you reckon I might as well leave out the PIR? It’s meant to be an office all year round!

Thanks!

PIR is a thermal insulator. A lot depends how comfortable you want to be and how much you wish to spend on heating. Also, you need to look at the way the construction is detailed, so that you don't have a build up of condensation within the framing. Foil sandwich PIR coupled with foil tape, makes an excellent vapour barrier. You would typically have this on the warm side, whilst the external clad (T&G) would have breathable wrap along with a gap behind etc.

 

[MNW67]

2 layers of r14 (3,5 inch) fibreglass

Are you proposing 7 inches of fibreglass insulation?

How important is the soundproofing to you. I have read previously that wall design is very important for sound. The same wall elements in different arrangements can give very different results.

 

[MNW67]

How important is the soundproofing to you. I have read previously that wall design is very important for sound. The same wall elements in different arrangements can give very different results.

@BerryNewbie

Just to follow up on that. I think I also read once that if you have windows, then they will let in a lot more noise than any wall. But it is a long time since I looked into these things.

 

[Notch7]

Hi guys,

I’m building my own garden room for all year round purpose. I wanted the insulate with PIR and add soundproofing on top. But I’m actually starting to doubt whether I need PIR at all! Without the PIR, the wall layers would be (from outside in):
- 40 mm tongue and groove timber
- 2 layers of r14 (3,5 inch) fibreglass
- one or two layers of 15mm acoustic plaster board.

Do you reckon I might as well leave out the PIR? It’s meant to be an office all year round!

Thanks!

It’s not clear from your description of the construction, but the correct timber frame detail is from outside:

1 timber cladding
2 50 x 25 vertical battens
3 breathable membrane like Tyvek housewrap
4 stud frame - with ply or OSB sheathing on inside or outside.
5 insulation in between the timber frame
6 vapour control layer
7 internal finish like plasterboard etc


With this construction the vertical battens creates an air cavity, any water getting through the timber cladding runs out the bottom. Also the air cavity create air movement behind the timber increasing its life span

with this construction once the breathable membrane is on the outside the structure is water and wind tight, the timber cladding is mostly decorative.


The log cabin type structures with very thick timber tongue and groove boards are a poor construction technique in this country, they trap moisture and lead to rotting.

 

[^woody^]

PIR is the best for heat insulation, so the more the merrier.

For a timber garden building, a single standard 12.5mm plasterboard layer and skim will be fine. 15mm acoustic board ever so slightly better. Bear in mind that acoustic linings on the internal face are really to stop sound getting out, not getting in.

You won't notice any difference in sound, or even achieve any unless you design the structure to deal with the sound - connection details, choice of materials etc