Insulating old walls?

[Agile]

I have a small room with 75mm stud and lath and plaster and vertical tiles and zinc external cladding.

This was built in 1926 when insulation was not important.

There are about 5 sq m involved.

Do you think I should try using the injected foam through small holes?

Or better making some larger holes at the top and drop down polystrene granules?

Or any other suggestions? Or dont even bother?

Tony

 

[AronSearle]

Is the zinc cladding direct to the frame, or is there a cavity.

Condensation could be a concern.

 

[Agile]

I expect the zinc is on some type of board. But dont know exactly.

Been like that since 1926 and no obvious problems.

Tony

 

[AronSearle]

It wont be a condensation problem now, as there is no insulation, so lot's of heat is lost through the wall, preventing it from occurring.

If it is direct to the frame (possibly onto spruce ply or more likely softwood boarding), and you insulate it, then condensation may occur directly behind the zinc cladding.

Or let me put it another way, if you know anything about timber frame I assume you know about vapour control layers (plastic sheet), ask yourself which side of the construction the VCL is applied to?

 

[Agile]

So what advice would you give?

Tony

 

[AronSearle]

Well you wont like it.

Rip off the zinc cladding, put insulation between the studs, maybe more on the outside (increasing the wall thickness), then put a breather membrane over that, batten out the wall, and then re-install or install new cladding over the battens so that you have a cavity.

If you insulate between the studs, with direct zinc cladding, the concern is that condensation will then occur on the back face of the zinc, this may only cause decay of the softwood boarding and not the studs, but you can see that's a bit iffy.

EDIT = I forgot that the softwood boards may also be providing racking resistance as there may be no cross bracing in the frame.

If you want a "make do" solution.....

Rip of the plaster, and install 10mm battens to the side of the studs on the face of the softwood carrying zinc. Then install rigid foam insulation (the battens maintain a 10mm cavity between the insulation and the boarding), use expanding foam to fill the gaps between the rigid foam and the studs (you wont cut them to size, and anyone who says they can is mistaken).

You then need to provide ventilation into that 10mm cavity, if it was softwood boarding you would remove the bottom board, and then re-install it on packers so that it kicks out slightly with an air gap. again if it was softwood boarding I would suggest installing a membrane to the face of the rigid foam, lapping over and down the sole/header plates (like mini cavity trays).

How you will do that last bit with zinc cladding I don't honestly know, but you could probably jerry-rig something.

The problem with this solution is that your studs are likely only 75mm deep, giving you 65mm of insulation (but then I think 60mm is a standard size?), it's better than nothing, but still lacklustre.

 

[Agile]

I cannot sensibly do anything internally which takes the wall further into the room because the uninsulated part is only a triangular part of the existing wall.

From what you are saying about the possibility of a condensation problem then I would conclude that polystyrene granules would be a better solution is they allow an airflow through the interstices.

Tony

 

[catlad]

Is it possible for you to take the plaster of the internal wall then over board the stud work with kingspan/celotex then add plaster board.

 

[catlad]

edit

 

[AronSearle]

From what you are saying about the possibility of a condensation problem then I would conclude that polystyrene granules would be a better solution is they allow an airflow through the interstices.

1. What airflow, you haven't indicated that there is a vented cavity behind the zinc, a timber frame of that period likely has direct cladding with no cavity?

2. The zinc gets cold, it can get colder than the air due to night sky radiation. This can cause condensation on the back face (as the zinc also acts as a vapour barrier rather than a breathable layer), it has not happened so far because the wall is uninsulated, and so the heat lost through the wall stops the back face from being to cold.




Download build desk, you can run a free trial version of it, it's a condensation risk analysis program.

Use it to model a 75mm stud with insulation and a vapour control layer to the outside, rather than the inside, it WILL tell you you have a condensation risk, and zinc would be worse than a plastic sheet.