Insulation and timber frame

[AndreK]

Hi all,
I'm new here but have seen some really useful discussions on these forums and thought it might be worth canvasing opinions on this. I'm not in the trades so sorry in advance if my terminology is off!

We moved into our current property about a year ago which was originally two timber framed cottages which have been more recently joined together. There have been several previous owners and various additions and modifications, many of which are not ideal for a property of this age or construction. We are in a conservation area; however, permission was granted in 2015 for external insulation which looks like it has been put directly over a previous cement render. A condition of planning at the time was that it it was also applied to the neighbour's property to avoid a step on the façade. On account of some damp, we've been doing some work internally and on stripping back the internal walls we've discovered a fair amount of rot and damp which is probably a combination of rising damp and condensation due to the poor breathability of the wall. There's also evidence of some previous attempted repairs where the sole plate has gone and the studs have been supported on brick, cement etc, none of which is at all ideal.

Of course we will need to look at repairing and supporting the frame but my question was more related to how best address the underlying issues. Whilst I would not have chosen to start with external insulation and cement render, I suspect this will be difficult to address and probably also very costly aside from complication of being in a conservation area. We'll obviously get some good advice locally but I was wondering if anyone on here had any previous experience or advice on how best to tackle the issue. We'll certainly plan to replaster internally in lime which will improve breathability but I'd imagine that there's still a risk of condensation given the nature of the external render/insulation. Presumably the better the internal insulation the better so long (as it is breathable) so not sure if warmcote could be an option but not sure how effective this is realistically likely to be. The external wall in this area of the house is (unsurprisingly) cold and it would be good to improve this but I'm guessing that any sort of infill (currently there appears to be nothing at all) would risk worsening the problem?

Thanks in advance for any thoughts or advice.

 

[Cubist]

What is the nature of the external insulation and how was it installed/fitted to the walls?

 

[AndreK]

What is the nature of the external insulation and how was it installed/fitted to the walls?

It was installed 10y ago and 2 owners ago but from the appearance and planning documents, it looks like insulation board (suspect EPS) either secured to the existing cement render with adhesive or fixings or a combination. From the inside I can see a couple of wall plugs which have come through the render but not sure if these are from fixings for the insulation or something else (only exposed the frame in places for the time being).

 

[Cubist]

Externally hung EPS insulation can, if it's Foil backed, be installed either to prevent external heat being transferred indoors or to retain internally generated heat - in the UK therefore it's most likely the latter. As even cement renders are not absolutely impermeable the net effect of their use can exacerbate the problem of moisture build up in the fabric of the buildings walls and contribute to their decay. As you have already found, the timber frame has suffered in the past and elements of the sole plate and some parts of the posts have already been lost. Hopefully the rotten wood was fully excised and the remaining timber treated to prevent new damage but.... replacing internal plasters and other wall coverings with breathable materials and paints could feasibly exacerbate the problem. Their more efficient transport of moisture produced indoors will almost inevitably increase the amount trapped in the fabric of the walls because there is no escape route and lead to new/additional decay.

In your shoes I would be planning on stripping off all that external insulation, properly addressing the major faults/damage to the timber frame and perhaps replacing any infill panels with more heat management efficient materials.

 

[AndreK]

Thanks, that's helpful. I agree, on the face of it the best option would probably be to strip off the insulation and cement render and start over and we'll look at the feasibility of this but, aside from the costs, I'd guess it may cause an issue with planning as it will result in a step in the front elevation between between the us and the neighbouring property and the initial application to insulate externally was rejected on this basis. To get around this, the neighbours insulated at the same time but we now have the reverse of the problem! Interesting though re the internal lime render and I see where you're coming from although presumably the net result will depend on the efficacy of the internal insulation and the humidity in the wall (although I appreciate that warmer inside air usually has a higher moisture content than that outside)?

The brick plinth is accessible as the external insulation does not run to the ground - looks like this has also been externally cement rendered and painted so presumably not helping matters. Internally there was also a radiator adjacent to the area of the wall where we've exposed the rotten frame. Not sure how much either of these are exacerbating the problem but I wonder whether it might be sensible to at least strip the cement render off on this accessible section in the first instance and perhaps relocating the radiator? (obviously aside from whatever's needed to address the frame!)

 

[Cubist]

I would not be overly concerned with the siting of the radiator but might consider replacing it if it is not one of the more modern variety that do not project heat wastefully toward the wall on which it is mounted - but even that would only provide a marginal improvement.

Do you mean the cement render on the brick plinth internally?

 

[AndreK]

Looks like lime plaster internally and cement externally. Re the radiator, yes I suspect it was probably heating the wall to a reasonable extent so perhaps contributing to condensation?

 

[Cubist]

Removing the render to expose the brick plinth outdoors may be helpful Insofar that it could then provide an avenue for moisture, whether absorbed from indoor human occupation/activities or perhaps rising from the ground below, to escape to the atmosphere. However, there is some risk attached to this as the brickwork may have been damaged, perhaps severely or even irrecoverably in some instances, due to trapped moisture damage. Its also possible that the bricks may suffer future spalling due to freeze/thaw cycling. May be best to leave this task to when/if you remove all the render outdoors.

Any heat sources will contribute to condensation and this will usually occur in colder spots on the walls and any windows in particular. Its unlikely to occur behind a wall mounted radiator - if anything it would be 'pulling' moisture out of the wall.