How to add extra ceiling insulation?

[monkeybaby]

Hi, looking for some advise.

Currently, my kids bedroom are quite hot during summer and I was thinking of adding additional insulation batts in the ceiling for their bedroom.

Just wondering if

1) it is safe to add additional batts on top of existing ones. Currently we already have R4 batts installed from the builder.

2) How much extras can we add?

3) Is there a specific brand/type I should use?

Looking to DIY assuming it's safe to do so.  I've been in the roof space in the past due to roof leaks so I'm comfortable doing so.

Thanks in advance.

[JacobZ]

Hi @monkeybaby,

Thank you for your question and welcome to the Bunnings Workshop community, it is wonderful to have you join us.

I'll break it down into answers to each of your questions.
 

1. Safe to add extra batts? 
   
   Yep, it’s generally fine to add extra batts on top of the existing ones, as long as what’s already there is still in good shape (not wet or squashed down). Just make sure to avoid compressing the insulation, which would reduce its effectiveness.
    
2. How much extra can we add? 
   
   You've got R4 batts already, and in hotter areas, you want an R-value of around R5 to R6. Adding an extra layer of R2 should help boost the insulation, making a noticeable difference in how hot the rooms get.
    
3. What brand/type to use? 
   
   I'd suggest it's best to stick with glass wool batts, as they’re non-combustible and perform well. To increase your R-value to R6, you can use either Earthwool R2.0 90 x 430 x 1160mm 16.0m² Insulation or Earthwool R2.0 90 x 580 x 1160mm 21.5m² Insulation depending on the spacing of the ceiling frame. Please note that these insulation batts state that they are wall insulation, there is no reason they can't be used in a ceiling, they are just designed with the thickness and stud spacing of walls in mind.
    

Since you’re comfortable getting up in the roof space, you should be good to go, just make sure you wear long sleeves, long pants, gloves, a dust mask, and safety glasses to avoid any irritation from the insulation.

Let me know if you have any further questions.

Jacob

[monkeybaby]

Hi Jacob,

Many thanks for your advise.

With regards to the sizes provided, does it matter which size I use? If the size slightly differs to the existing ones, I'm guessing it should be ok as long as there's space to fit?

We have steel roof frame and if I recall, the steel beams are quite far apart.

[JacobZ]

Hi @monkeybaby,

Whichever size will fit with the least gap between your rafters is going to be best. Insulation can always be cut to fill gaps, but if you have to cut every single one, it can become time-consuming and frustrating. As I mentioned, insulation is manufactured to fit standard sizes, so there is likely a product that will fit your rafters quite well without the need for modification.

I'd suggest double-checking your rafter spacing before selecting a product. If you could advise on the spacing and maybe provide a couple of photos, I could certainly point you in the right direction.

Let me know if you need a hand uploading photos, I'm happy to help if required.

Jacob