EWI 70's Timber Framed House

[StevoH]

Can anyone offer some sound advice on insulating a 70's timber framed house? Bought this house a year ago and in need of some repairs. Having new windows installed in a month or so.

Construction is timber framed with 70mm studs, spaces filled with mineral wool insulation. Plasterboard and skimmed on the inside, render over board over membrane directly fixed to outside of studs. Upstairs front of house has very 70's vertical tiles over board instead of render. There is no air gap between board/render and frame. No damp problems as far as I can see and house is not particularly cold although heats and cools quickly in winter.

Render is in need of repair in some places and window surveyor removed a few areas around windows - this has allowed me a good look at what's underneath.

So we are thinking of losing the 70's tiles and replacing with render and might as well re-render whole of house to refresh the look. I'm thinking there's a good likelihood that the board behind the render will also need replacing so is this a a good time to replace with insulation board e.g. 50mm EWI and render over that instead?

There seems to be conflicting advice over whether you can apply this over timber frame due to air gap but I'm 99% certain there is no air gap in this house. Is this then worthwhile or would the added insulation not make much difference?

Thanks to anyone who can help!

 

[AronSearle]

Handle with care!

Direct render onto timber frame, with no cavity, can work. But it is a really, really bad idea, and caused all manner of failures.

The advantage of not having much insulation, is that heat loss through the wall, helps to dry the frame.

The biggest mode of failure is moisture penetration around windows, as you have had new windows fitted, be very careful to ensure these have been fitted well. Lot’s of PVC cowboys out there who wouldn’t know a good fit if it smacked them in the face. Plastic reveals and blobs of mastic can hide all manner of sins.

In your case, consider the following options...

1. Insulated plasterboard, lose a bit of room space, but more insulation and reduced cold bridging, relatively cheap quick and easy. As mentioned above, this will reduce heat loss through the wall, making proper sealing around windows critical.
2. The more expensive option is to remove the render, add more insulation, then batten for a cavity and add a cementations render carrier board. You might want to consider either creating new window reveals, or re-fitting them further out into the line of insulation.



You also talk about replacing the board behind the render. This may be the structural sheathing, and can’t be replaced for non structural insulation panels.

 

[StevoH]

Thanks for the reply AronSearle! Windows are going in at end of November and being done by a well reputed local company so hopefully shouldn't cause any problems.

As far as the render goes, what would the likelihood be of getting the old render off without damaging the board underneath, especially if it's structural sheathing like you suggested it might be? And if the old render can come off safely, would fixing insulation board to this and rendering over be possible? I guess an advantage of this would be that insulation would be on the outside and heat from inside the house will still warm the frame reducing any damp?

Also, can anyone give any idea of ballpark cost? This is a 4-bed two-storey detached house approx 10m wide by 7m deep, so possibly 170m2 external walls incl. windows. I'd be interested to know cost of:
1) removal of vertical tiles and existing render then re-render whole house
2) as above plus insulation board with render over that.

 

[AronSearle]

Thanks for the reply AronSearle! Windows are going in at end of November and being done by a well reputed local company so hopefully shouldn't cause any problems.

If you do stick to the route of render with no cavity, ask them how they will seal the window junction, particularly where the horizontal cill joins the render. Ideally they want to be tucking the window in, and using expanding foam tapes, not just squirting mastic into it.

As far as the render goes, what would the likelihood be of getting the old render off without damaging the board underneath, especially if it's structural sheathing like you suggested it might be? And if the old render can come off safely, would fixing insulation board to this and rendering over be possible? I guess an advantage of this would be that insulation would be on the outside and heat from inside the house will still warm the frame reducing any damp?

Depends what the board underneath is. It is likely plywood, you can hack the render off and you will only superficially damage the top veneer. If any of the plywood is decayed, it will be pulled apart as you pull the render off, but then it should be replaced anyway. If you are going to insulate outside, and create a new cavity, you don’t necessarly need to remove the render that is there.

Can’t advise you on costs, but probably not cheap.

If it was my place however, I would be paying whatever it cost to do it, or getting rid of the property promptly. Direct render onto timber frame, with no cavity, no no no no no.

 

[NewCreationDan]

Hi Stevo,

how did you get on with your insulation project ,and did it work ? I've got the same issue and I'm researching a solution ?

Dan