Re-plaster of house

[RandomR]

Hi there,

I'm in the process of a refurb of a house. We've decided to replaster the entire house while taking down some wallpaper as it was pretty weak in places, taking it back to brickwork internally.

BCO visited for some structural changes, and mentioned we have to inform them of thermal changes due to the replastering.

Just reading this from the BCO application form:
Re-plastering or re-rendering to external wall of a room including insulation where more than 25% of surface

A few questions arise - since it's a mid terraced house, the external walls are on the front and back of the property. Majority of this is taken up by bay windows on the front, and french windows/kitchen window on the back - thus the actual "wall" coverage is pretty low

My question is how does this 25% surface measurement work, is it the entire wall (imagining no windows etc on the wall), or is it 25% of the remaining wall?

(Also just a daft question - this is talking about the internal plaster of an external wall right? - and not some external render/insulation which is facing the elements/outside air etc)

 

[mrrusty]

When I did my most recent refurb 4-5 years ago, where we live now, our BCO took the view that he wasn't bothered about this - he treated plaster as internal decoration, and in any case anything we could do to improve insulation would be better than it was.

However, I understand some BCO are more pedantic, particularly under the latest regs. Either way, if you are dropping the plaster, there are significant benefits in insulating. IMHO the challenge is to use the correct sort of insulation. I had discussions with my BCO about interstitial condensation risk, and the conclusion we came to was that internally insulated with insulated PB was OK because we had a ventilated cavity which would mitigate the risk of interstitial condensation by providing a method of evaporating any moisture in the wall fabric.

My own opinion is that it is a bigger challenge with a solid wall, and even bigger with an externally rendered solid wall that can't evaporate any moisture outwards. In this case I think there are good reasons not to internally insulate and risk trapping any condensation within a now colder wall. (any moisture-containing room air that manages to get to the cold wall fabric will condense within it, and if it can't subsequently evaporate will make the wall continuously wet) I have seen some breathable materials intended for insulating solid walls such as https://unitylime.co.uk/wp-content/uploads/2021/10/Technical_Manual_PAVADENTRO.pdf but never used it. I'm sure it is possible to internally insulate a solid wall successfully but only when all factors are considered.

If your BCO starts insisting on internal insulation on a solid wall, I would open up a conversation on interstitial condensation risk and see where it goes....

 

[RandomR]

Thanks for the response @mrrusty - Yeah looks like I had a trainee/under supervision BCO today (without her supervisor present) which was a tad frustrating

- Has to get her supervisor to confirm her findings on the foundations dug for the concrete pad were okay (even though they were all up to the width x depth required by structural engineer, even a tad bit deeper and wider in-fact). So was not able to give the greenlight on the day, and I'll have to wait for her to confirm with her supervisor.
- Since the beam was not measuring exact as 152x152, even though the SE requested 152x152x44UC (which has a different sizing) - she was not aware of these differences as expected all of them to be 152x152 exact (regardless of the weight class)

Alongside this, she was huffing about the internal re-plaster we plan to do etc..

So just worried how to get ahead of the game here and prepare as much for the next visits if they follow the same suit here. Would ideally like to avoid including unnecessary aspects for them to check upon if it follows this pattern.. wish me luck

 

[mrrusty]

In the past I have found a good tactic with pedantic people is to force them to detail their decision in writing. "OK, I hear what you are saying. I don't agree, but please detail your decision in an email so it is on record"

It does tend to focus minds....

I use this quite a bit in tenders when we get a draft contract that prescribes exactly what should be supplied in a proprietary manner because they have used a competitor to help draft a specification. I just ask for clarity in writing whether we have design responsibility or do they because they are telling us exactly how to do it. Usually results in unwinding of the prescriptive elements of the tender spec!

 

[wessex101]

OP needs to read Section 11 of Part L - Renovation of a Thermal Element.

In this case the thermal element is the external walls only measured internally, just the external walls not windows or doors. So it is more than 50% of the external walls thermal element (not including doors or windows) or more than 25% of the external envelope (including walls, doors, windows etc.)

The get out clause is usually that adding insulation to achieve the required U value is not "economically viable".

 

[RandomR]

Thanks all

I'll take a read of the exact wording to understand further. Economically viable response may be my go-to for now, as the risk of interstitial condensation seems to be high on the wall, and I don't want to forever battle condensation behind any internal insulation installed.

Unfortunately, I have radio silence and no response to emails/phone from any BCOs from the council - so just a waiting game now while I proceed with caution on the works

 

[noseall]

In the past I have found a good tactic with pedantic people is to force them to detail their decision in writing.

The rule is already in writing and has been around for a while. It's not pedantry but rather an overlooked (by renovators) regulation.

 

[noseall]

Unfortunately, I have radio silence and no response to emails/phone from any BCOs from the council - so just a waiting game now while I proceed with caution on the works

I would proceed with the the view that you may have to insulate internally - i.e. switches etc may need to stand further proud of the masonry.

Removing plater back to brick, is renovating a buildings' thermally accountable fabric. The 25% rule applies.