Workshop Floor Insulation

[MrD]

Hi,

Just started my new workshop build and wanted some advice on floor insulation. The floor will be 2*4 joists at 600mm centers with 25mm redwood floorboards on top. This is all set on bricks off the ground to allow air flow.

I want to add insulation before I add the floorboards however I am more concerned with sound than heat loss.

Many people use the polystyrene slabs cut to size but I have read these are no use in sound reduction. I was looking at using the higher density rockwool slabs like RWA45 or RW3/4 but I am unsure if these will be suitable for the purpose?

Any thoughts would be greatly appreciated.

Mr D

 

[MikeG.]

I would avoid polystyrene.......it is a poor product in my view. The mineral wool insulants help with sound deadening, but are awkward to hold properly in place. PIR foil-faced boards (Kingspan, Celotex) will give you the best thermal performance and are much easier to fix in place than mineral wool.

However.........

..........what worried me is you floor design. Four by twos at 600 centres is the sort of spec. to suit an evenly and lightly loaded floor spanning about 4 feet!!!

Please tell me that there is intermediate support, say every 900mm?

Mike

 

[MrD]

Hi Mike,

Do the PIR boards help with sound? They do look very easy to work with.

You are correct I will be adding supports probably more than every 900mm.

During my last build I jumped up and down on the timbers and if I felt any flex I added more support - not very technical but it worked for me!
I am also using c16 graded timber which should help.

The reason for not using bigger timbers is overall height - it is close the boundary so the new planning rules mean I need to keep it below 2.5m within 2m.

Thanks,

MrD

 

[PAC1]

Mr D

If you increased your 4x2 to 5 or 6 x 2 you can install extraction ducting between the joists. Just a thought.

 

[CWatters]

Why are you worried about sound going downwards? You got someone living under your workshop? :shock:

 

[MrD]

Trolls

Seriously from what I read sounds gets out from everywhere and you can have 30cm of soundproofing in the walls and it can be ruined by a bad fitting door.

Just trying to get my workshop as quiet from the outside as possible!

 

[MikeG.]

Do the PIR boards help with sound?
MrD

The Kingspan-type boards only help a bit.

The best way of fixing them in place is to cut them undersize by about 10mm all round, and fill the gap with spray foam. The lack of gaps that this will produce will really help.......but the best compromise might be to have 50mm of Kingspan at the bottom of the joist depth, with 50mm of mineral wool sitting on top of it and hard up under the floorboards. The key thing for sound deadening is to make sure there are no gaps, so cut the rockwool slightly oversize.

Mike

 

[MrD]

Mike,

That sounds like a good idea - the mixture of the 2.

And you are correct - sound deadening rather than sound proofing!

Cheers

Mar D

 

[CWatters]

Part E (sound) of the Building regs has example floor constructions for floors between dwellings. Perhaps worth a look.