How to install underfloor insulation?

[michellehoo]

Hi,

I’m looking at installing underfloor batts but the only size available are the 420mm floor shield earthwool batts. The space between the timber beams is 455mm. It will be installed under a raised posted house with a children’s play area, garage, laundry and storage shed under it. Will we also need the wind wash barrier? 

Thanks,

Michelle 

[Jewelleryrescue]

Hi @michellehoo 

In the Earthwool range there is the Floor shield floor batts at 420mm wide only R2.5.   where as you require 455mm, The floor insulation has a backing on it so exposed under floor installions is not effected by wind ie blown or sucked out of position so much. The same barrier canhelp lock in the insulation fibers as I see it.   Your planned insulation area sounds fully enclosed  and not exposed to the wind so a Wind Floor shield feature is not really required the way i am seeing this possible situation.

As your under floor area also living space you may  choose to use panelling or Gyprock to seal in any installed batts to improve livability. As typical batts use  unsightly  straping to hold them into place. I also would not want to expose family to fibers constantly.

As your floor spacing are 455mm of a different sizing to the products avaliable It would seam 430  or 580 mm wide are the most prevalent sizes so cutting batts to your floor joist sizing is  unavoidable unless you can find a R2.5 batt of the exact width of 455mm.

A 580mm batt wide you can cut down too 460- 470mm for a firm fit with an offcut of 110-120mm.  4 of these offcuts put together will  fit a space  of 455mm tighly . as long as all the spaces enclosed  firmly .   You will still need packing tape to hold them in place,

So consider buying a wall batt of R2.5 or greater at sizing 580mm wide trimming and re using he offcuts. as one possible trimming solution. also  consider a  gyprock roof option post instalation

EG bunnings 

Earthwool R2.5 90 x 580 x 1160mm 9.4m² HD Insulation SoundShield Wall Batt - 14 Pack   I/N: 0810603                         $ 115

[michellehoo]

Thanks for the information. Do you know if the wall batts have a coating to stop fall out like the Floorshield? 

We would rather not have to cut the batts. Have you had any experience with other brands that sell 470mm batts? 

[EricL]

Hello @michellehoo

Welcome to the Bunnings Workshop community. It's pleasure to have you join us, and thank you for sharing your question about floor insulation.

It's great that you've received excellent advice from @Jewelleryrescue. I've been in contact with our supplier Knauf Insulation and I've relayed your situation. I'm sorry but in order to fill the gap that's left a portion must be cut off to fill the space. The wind wash barrier is actually a coating that's been applied to the front and back of the insulation and is not a product that can be purchased separately.

However, another alternative is to use the Expol 1200 x 470 x 60mm Polystyrene Insulation Panel - 10 Pack. This floor insulation can be cut down very close to the size that you need. It's held in place with a plastic bracket system and does not need strapping.

Here are some handy step-by-step guides: 

• How to install polystyrene insulation
   
• How to install underfloor insulation batts

Please remember that when handling insulation make sure to wear personal protection equipment such as goggles, gloves, dust mask and a thick long-sleeved shirt. 
 

If you need further assistance, please let us know.

Eric

[michellehoo]

Hi Eric,

Thanks for your reply.

Do you think it would be ok to fit the floor shield to size by cutting 4cm strips to fit the 445mm space between beams? Will we need to use packing tape to stick them together or should the strapping tape do the job?

Would you recommend additional gyprock ceiling to cover the insulation if we use the space for a playroom and garage? 

[MitchellMc]

That will be fine, @michellehoo. The idea is that the batts are compressed into the space securing them, and the strapping is just to ensure they don't fall out. There shouldn't be any need for additional tape even with installing the 4cm strips alongside the full batt.

Sheeting the underside of the floor with Gyprock plaster is not necessary, but it will certainly improve the area and make it feel more like an actual room.

Please let me know if you have further questions.

Mitchell