How to top up roof insulation?

[dannyp]

I have existing batts in the roof but I'm pretty sure they are only R2.0 as I found an unused pack left in the ceiling.  I'm thinking of adding additional insulation on top of it, but have some questions -

• If I add earthwool R6.0 on top of the existing one, does that mean that I have achieved something like R8?
• I have seen different forums where they advise to install the new insulation sideways to the existing one, where others say to run the new insulation in the same direction as the existing one.  Which is best?
• I have LED downlights, can I just put the insulation over the top of the downlights or does it need some sort of cover?

[Jason]

Welcome to Bunnings Workshop @dannyp. it’s great to have you join the community.

Our resident Bunnings D.I.Y. experts will be back on the site on Boxing Day. In the meantime, let me tag some other helpful members: @R4addZ, @Dave-1 and @Nailbag.

You should also find helpful advice in previous similar discussions on the site like this one - How to add extra ceiling insulation?

Jason

[Dave-1]

Good Afternoon @dannyp 

I remember reading somewhere that you should remove the old before you put in the new. However I cannot find that article. I think I would remove the old stuff in my ceiling and replace the lot. Mainly because the old stuff may be uneven in thickness, have gaps in the install (between other bats, beams, edge of the roof) and by installing over them it wont be consistant. "I am holding my hands up as a open hand either or showing" lol I have old bats that have been water damaged, aged. So I would go the route to "know" exactly my thickness I have.

As to installing over downlights. I dont like the idea. I do not know the ruling but it does make me uncomfortable.

If you work in a ceiling space I always suggest to turn off the power to the whole house (all power, stove, lights hot water) just to err on the side of caution.

Dave

[Nailbag]

Hi @dannyp 

A1. I don't know myself, other than I'm pretty confident it's not that simple.

A2. Personally I can't see any advantage or disadvantage in which way you run them. I would be putting them crossways though to the existing as they may lay better. I would concentrate on main living areas to save on heating and cooling

A3. If they are modern 90mm (give or take) LED down light with or without a transformer, then though generally not required I like to make a small hole around them in case I need to access without insulation getting in the road. Plus some models do get warm.  If they are the large ones with globes in them, then you need to keep them away due to the heat they generate. Often you will see old cardboard boxes cut out to create a barrier, but no cover. Just open to the air.

Merry Christmas

Nailbag

[R4addZ]

@dannyp 

Ok so my 2c worth is the loading on your ceiling What additional weight will you be adding into the ceiling if you have both and should it happen how much more weight would the insulation hold if you had a leak in the roof. LED downlights may well be Ok covered with insulation but if they have transformers, I would be putting them on non imflammable material above the insulation.

On a lighter note, did you know that the American military invented the word Famable because they had so many fires because recruits (under educated ones) thought th "Im" in the word imflamable meant it wouldn't burn!

[AlanM52]

Hi @dannyp,

I took advantage of the roof insulation Government initiative to upgrade our insulation because the original rockwool (blown in) was as flat as carpet.

Speaking to the install guys they usually remove the old batts and replace with new but in my case the advise was to just leave the the old (what was left) and lay down the new batts.

Covering the downlights depends on their rating:

• IC-Rated (Insulation Contact): These lights are designed to touch insulation and can be fully covered, ensuring safety and better thermal performance.
• IC-F or IC4 Rated: Indicates they are safe to be abutted and covered with insulation, with IC4 being a common modern standard.
• CA Rated (Ceiling Awning): Can be next to insulation but not covered, requiring a gap.

Check what type you have and take it from there and I would wear protective coveralls and at least a P2 Mask.

Cheers

[JacobZ]

Hi @dannyp,

Welcome to the Bunnings Workshop community, it is wonderful to have you with us.

In theory, R2.0 plus R6.0 equals R8.0 because thermal resistances add up. However, in practice, gaps, compression, thermal bridging through framing, air movement, and installation quality reduce the effective R-value, so the actual performance is lower. Basically, in an ideal scenario, yes, the R values would simply add together, but in reality, external factors mean both insulation batts won't perform perfectly, so the r value will be reduced.

In theory, if you run them in alternate directions, any gaps in the lower level should be covered, which could slightly reduce air gaps, but the difference would be minor. I think it is more important that you run the second layer whichever way gives the best coverage.

@AlanM52's advice about the downlights is what I would be looking at here.

Also, as he mentioned, protective coveralls and a mask are a must. Trust me, there is nothing worse than being in a hot ceiling cavity, building up a sweat and then having fibreglass insulation stick to your skin.

Let me know if you have any further questions.

Jacob

[AlanM52]

CC: @dannyp,

I forgot to mention and with personal safety in mind push back roof tiles to provide ventilation and light.

If you don't have any timber boards lying around buy a few 1.8M fence palings - crawling boards.

I prefer not to use kneepads because there is less feel for where the knees are being located.

Cheers