Renovation - how far to go?

[Rob55]

Hi

 

I have a 2 storey house of 1980's construction.  Inner/outer walls are constructed of 100mm concrete blocks, and a 70mm cavity fully filled with bonded white beads.  Approx u-value of 0.46 and no air tightness detailing!  I plan to completely gut and renovate this house to a high standard - new windows with good thermal detailing, insulation upgrades and if possible air tightness improvements where possible.  At the moment I have planning permission and am moving on to detailed construction drawings for building control, so need to make the decisions now regarding insulation.

 

So, what to do?

 

52.5mm Insulated Plasterboard, approx U-value 0.22.  Easy to put on, and internal walls will need re plastered anyway due to window re modelling.  However, I am concerned about condensation as I have heard a few horror stories about the dew point moving within the room, and I don't know how to stop this from happening.

 

100mm External Wall Insulation, approx U-value 0.19.  External walls will be getting re-rendered anyway, so the main cost is just the insulation and labour.  But I want granite window surrounds and heads, so I don't know if they can be fitted with 100mm EWI.  

 

 

Can either method be used to improve air tightness?  I know that there will be a lot of air weaknesses in the current construction - plug sockets, the void between floors, etc etc.  

 

Any other ideas that could be done to improve what's there?

 

Cheers

 

Rob

 

 

[Ferdinand]

Welcome ROB - suggest an intro in the intro section, and perhaps a project blog (PM an admin).

 

You can do airtightness with either, but don't overfocus on the walls - you will get better resutls first with floor and loft if it is already 0.46.

 

Do not forget the bit of wall between the floors, though.

 

Work out your whole programme before you start, and build a thermal model using the @JSHarris spreadsheet produced by a member here. Take time to think it all through and do your homework.

 

Of those go internal - external will cost at least 10-15k, and by the time you have done 2G, normal insulation plus underfloor, etc, new CH, and so on it will not be worth it unless you get a grant, or there is a very good reason. Perhaps for a forever house. I have costed up for 4 or 5 over the years, and it has never been able to justify the cost.

 

Then spend money on doing all the obvious usual things, and you should get to an EPC B or so.

 

Two threads, about reno of a 1970-ish bungalow in 2017:

 

And some possible quick wins.

 

Ferdinand

Edited October 3, 2019 by Ferdinand

[Rob55]

Hi @Ferdinand

 

This will be my forever home, so I am prepared to go the extra mile.  Sorry for stupid question but what is 2G?

 

I am thinking internal insulation will be best bang for buck, and seems like it would have the best response to heating by keeping that heat within the room.  But definitely worried about shifting the dew point and causing condensation/mould within the rooms.

 

I will definitely be putting in plenty of loft insulation, easy win in a 2 storey house, there is already a layer of wool up there and I can easily add 2 more layers of 200mm each for low cost and zero labour cost.

 

As for the floors well that's a bit more tricky as it would require taking up the screeds and existing eps (I think it has 50mm at best) and replacing with something high density like Kingspan Kooltherm and a liquid screed in order to maintain floor heights.  Added benefit would be that I could put down UFH in the process, but only after the labour costs of ripping out all the old floors.

 

Keep the ideas coming!!

 

Cheers

 

Rob

[Ferdinand]

2G double glazing.

3G triple.

 

If you take what us in there out, there should be a local service that will fit 250mm for free.

 

You also need to consider ventilation if you insulate. You can model dewpoint, however. My normal approach (to solid walls) is 50mm of Kingspan plus a vapour membrane on the warm side plus plasterboard and skim, but there are many views on that.

 

On the thread I linked I did not do that for room size reasons, and that the u-value was already down to 0.55 due to cavity wall insulation.

 

Consider raising the floors, and put a floating floor over the top. Needs modelling. PIR or even aerogel? Plus one of the 18mm deep ufh systens? I gained about 60mm by trimming doors, and leaving existing frames.

 

Ferdinand

 

 

 

Edited October 3, 2019 by Ferdinand

[MikeGrahamT21]

EWI is my system of choice, sounds like a similar house construction, if you are pretty handy, and it sounds like you are, you could do the majority of the work yourself and save yourself a fortune. Like me, you will have medium dense blocks, and the really thick galvanised wall ties they used to use back then, basically the perfect thermal store, in my case I'm planning on using it, but I don't have as much area to cover as im in a bungalow. EWI also has the added benefit of giving the exterior of your house a brand new facade, and giving projection from the elements, preserving your building, good if you are in it for the long run.

 

As for the sills and heads, have you looked at foamstone? This may well fit with what you are looking for.

 

Floors, I would say AVCL taped up the walls above where the finished floor line will be, 50mm PIR or Phenolic board, taped, and chipboard/osb laid over the top.

Done a rough model above, hope I got the right materials, gone on what you said.

[joth]

One benefit of getting someone else to do the EWI insulation is they can 5% VAT rate it (materials and labour) -- so long as they're not doing it as part of a larger project.

[Rob55]

Yes if I go EWI, I will install the insulation myself. It seems handy enough. The outside of the house will be getting thin coat render anyway, so the overall insulation cost is definitely manageable. And it seems to kill all the wall based cold bridges, leaving us to concentrate on window detailing and floor/ceiling detail.

 

i had seen foam stone before but no experience with it, architect had a sample but said they have never used it, anyone know if it’s any good?

 

I had Kingspan run some calculations and if I go for internal insulated plasterboard, I have no risk of interstitial condensation at 62.5mm (and even at 102.5mm) so at least that’s still a good option if I don’t go EWI. 

[Rob55]

Just looked at Kingspan’s email and they have actually done an EWI calc based on only 50mm EWI (Kooltherm K5 so it’s the more dense board) and it’s bringing the U value down to 0.21. This could be a compromise that would work with my granite sills and heads! 

[MikeGrahamT21]

I wouldn’t go K5 for EWI, I’ve heard stories of it shrinking post install leaving cracks everywhere, they nearly pulled it from market at one point. Plus it’s expensive.

 

minimum 100mm eps is far cheaper as long as you have the overhang on soffits to cope with it, and will probably get you an even lower uvalue. Eps also has a degree of allowing moisture vapour to escape, albeit slowly, where as phenolic does not allow passage of water full stop