How do I insulate this wall?

[AliG]

I discovered a while back, that a small area of the house was accidentally not insulated.

 

There is a way that appears to be an internal wall from one side, but the top half of it backs onto uninsulated loft. No one realised during building works, I only noticed it with an IR camera.

 

After much procrastination I just cut a hole in the ceiling so that I can access the loft area behind the wall. It was in an area of loft with no access.

 

The area of the wall is around 12sq metres. I had a load of spare EPS and PIR from my parents' house which I was planning to stick to the back of the wall.

 

Now that I have been up there, I can see that there are roof joists around 50mm off the wall. I would have to make dozens of angled cuts in the insulation to stick it to the wall.

 

Looking at it my thought is that I get cavity batts and squeeze them behind the joists so these actually hold them onto the wall. It also means I won't have to cut up the insulation to get it up there.

 

It is a very small area relative tot he whole house and it is not exposed to outside, so I think this modest amount of insulation would be good enough.

 

Does this make sense?

[AliG]

I went up and measured the exact gap behind the joists, it is 45m.

 

I don't know if a 100mm batt would compress enough to go behind that. I could use 50mm, but that is not a lot of insulation.

 

I have some 100mm loft roll lying around which I could maybe get up there then squeeze behind the joists.

[joe90]

The trouble is if you squeeze all the air from a bath etc you diminish it’s insulation thin PIR  would be better.

[AliG]

True, but I was thinking this would only be in the small area behind the joists. I suspect that loft roll might be better as it is not as firm so would only be squeezed where the joists are and pop out either side of them.

 

I am not sure if I can consistently get 40mm PIR behind the joists. If I could I wouldn't have to stick it down, I could wedge it with the joists.

 

I was thinking maybe 100mm loft roll partly squeezed behind the joists then I could roll another 100mm across the face of the joists and hold it in place with some pins into the joists. I guess I could use PIR then 100mm also.

 

I have some thin PIR kicking about as well as the loft roll, maybe I need to experiment with both in the morning and see what works best.

[nod]

Gypliner is quick and easy to install

Simply push the batts between each strut 

[AliG]

Thanks but I think the joists would get in the way.

 

Also I don’t want to be building a frame up in the loft.

 

For full disclosure the wife has been complaining about the massive pile of insulation in the garage and I have promised to do it this week so trying to keep it quick and simple.

 

There is not a lot of air movement up there and the wall is air tight so I don’t need to worry much about air tightness. Mainly looking at losses straight through the wall.

 

As the space is not directly outside I’m not sure how bad the heat losses are. However the wall shows as consistently cooler on IR during the winter so there is definitely some loss.

[AliG]

Started, first job is tidying up in the roof space. Removing insulation wrapping etc that had been left up there.

 

I recommend everyone has a root around in their roof. Whilst the insulation has been applied to at least the 300m thick specified, if not more, it has been quite untidily fitted with some small areas missed, especially around pipes.

 

I started to move it around to fill these areas in, then realised that I can see places I can stand more easily where the insulation is missing, so I will insulate the wall first then rearrange the insulation.

 

I have been wearing one of these-

 

https://www.screwfix.com/p/stanley-lite-pro-one-size-reusable-half-mask-ffp3-r-d/473kc

 

What a difference a dust mask makes. Insulation is incredibly dusty and normally after I have been in the loft I feel like my throat has been sanded.

 

It is extremely sweaty work, so I cannot wear eye protection, it steams up too much. My glasses keep falling off, I need to figure out how to use the dust mask straps to keep them on.

[gaz_moose]

its worth buying a cheap disposable coverall suit too as it gets all over you. when i did mine i also wore marigold gloves taped at the sleeves. then do the work when its cool. 

[joe90]

1 hour ago, AliG said:

that I can see places I can stand more easily where the insulation is missing,

It’s the attention to detail that makes a job “proper”. 

[AliG]

My wife really wanted me to pay someone to do it but I knew they wouldn’t take a lot of care over it.

[AliG]

29 minutes ago, gaz_moose said:

its worth buying a cheap disposable coverall suit too as it gets all over you. when i did mine i also wore marigold gloves taped at the sleeves. then do the work when its cool. 

Yup gloves and long sleeves are a must.

[AliG]

So only 25mm PIR fits behind the joists.

 

A couple of joists are too tight even for that.

 

About 2/3 done. The hardest bit is the diagonal cuts where it won’t go behind the joists.

 

 

[saveasteading]

Some mineral wool batts will tear down the middle because they use denser stuff on the outside . Otherwise squeeze it in as it's a lot better than nothing.