Deep Retro-fit.

Pat Smith

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We are undertaking a deep retrofit project on a 1970 detached bungalow. There is currently a subfloor that a builder is recommending we fit a new 150mm concrete floor on 100TF insulation on a Radon barrier. Is this the most cost-effective option What other options are there ?
 
I think that is the only way you can really get sufficient insulation into the floor, and without addressing the floor, you lessen the effectiveness of the rest of the work.
 
OP, I would be a bit concerned that you are asking quite a basic question on your deep retrofit project. If you have someone advising you then would they not be best placed to advise. If not, why not?

Agree with Leo above that the floor weakness needs to be dealt with. You do have another option and that is to insulate/airtighten the existing floor but this decision depends to a certain extent of what other measures you are undertaking. For deep retrofit to be successful you need to take a holostic approach and not look at one measure in isolation.

And to put in perspective what I'm getting at, I live in a deep retrofitted 1970's bungalow, which you couldn't heat past 18 degC when we originally bought it. It now takes very little energy to maintain a comfortable temperature and even overheats during a power outage when too many candles are lit. Yet, the one thing that was not touched for various reasons during the retrofit works was the original floor slab (still uninsulated).
 
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And to put in perspective what I'm getting at, I live in a deep retrofitted 1970's bungalow
I'm looking at upgrading the insulation in our 1960s bungalow. Could you give some details on what you focused on Micks'r?
 
I'm looking at upgrading the insulation in our 1960s bungalow. Could you give some details on what you focused on Micks'r?
First off, while insulation is important, it's not the be-all and end-all its often made out to be. Very often too much emphasis on insulation and not enough (or none) on airtightness and ventilation.
So, you need to understand first the 3 forms of heat transfer (loss) i.e. conduction, convection and radiation and address each one with insulation, air tight measures and glazing options respectively. Also, as you add insulation the role and impact of thermal bridging (relatively high conductive material bridging your insulation layer) becomes very significant not only for heat loss but also potential for mould growth internally. Finally, you need to ensure sufficient ventilation is provided to exhaust the internally generated moisture from normal occupant activities.
So, what we did was
1. Tested the house for air tightness to understand all the air tight issues (>10 m3/hr/m2@50Pa). The weaknesses then were addressed in a methodical way and incorporated into any other improvements - basically all junctions and penetrations of the external thermal envelope were air tightened using a variety of air tight materials. Final test show huge reduction to less than 1 m3/hr/m2@50Pa, >90% improvement!
2. Whole house mvhr system installed in the attic space
3. 300mm cellulose pumped into the attic
4. 200mm rockwool ewi extending down 600mm below the finished floor and up past the soffit to meet the attic insulation. By going down past the floor and up past the soffit, the linear thermal bridges were pretty much eliminated and also the need to insulate the original concrete floor slab was mitigated (personally, I prefer a slightly cooler floor slab under my feet when everything else in the space is warm, ... I don't like underfloor heating for this reason). We went with 200mm ewi for 2 reasons: 1. we had a 450mm soffit so 200mm still left a 250mm soffit and 2. doubling the insulation thickness added only about 10% to the ewi cost.
5. Replaced all windows the ph certified units and installed them flush with the external wall outer surface so that the ewi overlapped the thermally broken frames, again eliminating the thermal bridges around the opes.
 
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I agree with everything you have said and the detailing you mentioned. Would you care to name your advisor for that build?
 
I agree with everything you have said and the detailing you mentioned. Would you care to name your advisor for that build?
I was the advisor. (I'm an engineer who has specialised in domestic heat loss mechanisms and solutions)
 
First off, while insulation is important, it's not the be-all and end-all its often made out to be. Very often too much emphasis on insulation and not enough (or none) on airtightness and ventilation.
So, you need to understand first the 3 forms of heat transfer (loss) i.e. conduction, convection and radiation and address each one with insulation, air tight measures and glazing options respectively. Also, as you add insulation the role and impact of thermal bridging (relatively high conductive material bridging your insulation layer) becomes very significant not only for heat loss but also potential for mould growth internally. Finally, you need to ensure sufficient ventilation is provided to exhaust the internally generated moisture from normal occupant activities.
So, what we did was
1. Tested the house for air tightness to understand all the air tight issues (>10 m3/hr/m2@50Pa). The weaknesses then were addressed in a methodical way and incorporated into any other improvements - basically all junctions and penetrations of the external thermal envelope were air tightened using a variety of air tight materials. Final test show huge reduction to less than 1 m3/hr/m2@50Pa, >90% improvement!
2. Whole house mvhr system installed in the attic space
3. 300mm cellulose pumped into the attic
4. 200mm rockwool ewi extending down 600mm below the finished floor and up past the soffit to meet the attic insulation. By going down past the floor and up past the soffit, the linear thermal bridges were pretty much eliminated and also the need to insulate the original concrete floor slab was mitigated (personally, I prefer a slightly cooler floor slab under my feet when everything else in the space is warm, ... I don't like underfloor heating for this reason). We went with 200mm ewi for 2 reasons: 1. we had a 450mm soffit so 200mm still left a 250mm soffit and 2. doubling the insulation thickness added only about 10% to the ewi cost.
5. Replaced all windows the ph certified units and installed them flush with the external wall outer surface so that the ewi overlapped the thermally broken frames, again eliminating the thermal bridges around the opes.
Few questions if you wouldn't mind, maybe we need a separate thread but sounds like a great project!

  • Once you got the house tested for airtightness (which I understand is a blower test), how did you go about identifying weaknesses in order to address them? I haven't come across anyone who provides such a service or even a decent guide of how to go about it.
  • How did you continue your EWI above the soffit?
  • Could you name a supplier for passive house certified windows - what sort of a difference (performance & price) would you be talking Vs SEAI approved double / triple glazed windows?
  • Can you explain your window detail more? You moved the windows all the way forward to they're flush with the outer edge of the insulation? How did you install the windows in that case? Or you insulated over the window frames once they were installed?
 
Few questions if you wouldn't mind, maybe we need a separate thread but sounds like a great project!

  • 1. Once you got the house tested for airtightness (which I understand is a blower test), how did you go about identifying weaknesses in order to address them? I haven't come across anyone who provides such a service or even a decent guide of how to go about it.
  • 2. How did you continue your EWI above the soffit?
  • 3. Could you name a supplier for passive house certified windows - what sort of a difference (performance & price) would you be talking Vs SEAI approved double / triple glazed windows?
  • 4. Can you explain your window detail more? You moved the windows all the way forward to they're flush with the outer edge of the insulation? How did you install the windows in that case? Or you insulated over the window frames once they were installed?
1. Yes, blower door used. With the correct weather conditions, a thermal imaging camera, trace smoker and, most importantly, an experienced surveyor/tester all major weaknesses are readily identifiable. As I do these surveys for a living, this was the easy part :) .
2. Remove the soffit and continue the ewi up to top of the external leaf. Then, using earthwool or similiar, bridge the gap between the ewi with the ceiling insulation. We used a fully breathable ewi (rockwool) so it was straight forward to achieve. Supplemental attic ventilation was provided by coring the gable walls.
3. Can't name them here . I'm not aware of "SEAI approved" suppliers. The units are Passive House certified and were extremely competitive. I had my own builder install them though;)
4. No, they were flush with the outer edge of the original external wall leaf, then the ewi overlapped the frames thus eliminating the tb.
 
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Thanks for that, re: no.4, would installing the windows in their old position, prior to the ewi, not have an end result of more insulation over the window frames in any case? The ewi installers would hardly have left the frames bare in either position?
 
everything I've read about EWI says that you should move your windows out to meet the insulation, but any houses I've seen with it done, they haven't bothered. How much of a difference does it make?
 
Thanks for that, re: no.4, would installing the windows in their old position, prior to the ewi, not have an end result of more insulation over the window frames in any case? The ewi installers would hardly have left the frames bare in either position?

You have to address cold-bridging and the condensation/ mould issues that causes. Moving them out eliminates those issues, but EWI installers are slow to do that as it's difficult to move windows without damaging them.
 
Thanks for that, re: no.4, would installing the windows in their old position, prior to the ewi, not have an end result of more insulation over the window frames in any case? The ewi installers would hardly have left the frames bare in either position?
By not moving the windows out you are left with a significant thermal bridge, the consequence of which is a real risk of mould formation internally on the reveal.
In addition, in out case of 200mm ewi plus 100mm external leaf, there would be an external reveal depth of 300+mm which both aesthetically and solar gain wise is poor.
Also moving the windows out means that we have quite a deep internal reveal which can be useful.
 
@Micks'r wonder if you can answer this, just an opinion, like "if it was my house...". Apologies for hijacking the thread, I will delete the post if not acceptable.

House is 1920s, 2 storey end of terrace, suspended wooden floors in hall & reception rooms, solid floor in return (not insulated at ground level), no insulation apart from some DIY rockwool in attic, red brick so EWI solution not an option.

Planning a refurb + 2 storey extension. Big focus on making it more snug. Includes attic conversion (so will resolve roof insulation). New windows throughout. Extension will probably have EWI, with internal insulation on existing internal walls. Need to re-wire, adding new bathroom, moving kitchen, new gas boiler (rads are good). Will need to dig out and insulate floor of return room at ground floor level.

Main thing I can't make my mind up on is the suspended floors. My inclination is that while gutting the house we should backfill the void in hall & reception rooms. Purpose is to stop draughts, improve insulation, avoid any rotting or rodent issues in the future. If we don't backfill, we'd probably need to lift the current boards and insulate/draughtproof - feels like a better option to backfill.

Wonder what you think about that choice?

If doing that, is it mad not to put in underfloor heating? Increasingly people will be spending more time in the house, working from home etc. I'm cautious of putting in UFH based on running costs, "heating always on" but it might be nice to have a reasonable ambient temp all the time. Not interested in A2W/heatpump, so it's likely to be gas powered. Note, we would have rads upstairs. We have a Nest so could potentially add another Nest and have UFH zone and Rad zone.

Are we mad to consider putting down all the backbone for good UFH and not do UFH? Would be nice not to have rads everywhere.
 
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House is 1920s, 2 storey end of terrace, suspended wooden floors in hall & reception rooms, solid floor in return (not insulated at ground level), no insulation apart from some DIY rockwool in attic, red brick so EWI solution not an option.

Take a look at this guide, it provides decent guidance on what should be tackled first in terms of return on investment for a lot of the common Irish house types.
 
"If it was my house" I would take a fabric first approach. I.e. optimise the thermal envelope against heat loss and moisture buildup. Then I would ensure I'm adequately ventilated and only then think about how to supply the little amount of energy (heat) required to maintain a continuous comfortable temperature. Underfloor heating would not be part of my plans for personal reasons. I would then choose my professionals & contractor very very very carefully.

Existing house:

1. Do you have a target for air tightness? If not, why not? If you don't understand its importance, then research it until you do. This is critical. Special attention would be given to the attic conversion as these are well known to adversely affect the rest of the house when ignored. Any efforts to improve the insulation values of the thermal envelope fabric may well be wasted if the air tightness is poor. My air tight target would be <1 m3/hr/m2 which is 5 times tighter than current b.regs and I would be confident of achieving this in a refurb scenario.

2. I would thread carefully with the insulation specification especially on the external redbrick solid walls. Depending on what's there currently, I would likely use a thin diffusion open product on the internal of the walls, such as Calsitherm. I would be paranoid about moisture buildup in my walls and also cognisant not to introduce unnecessary thermal bridging. I absolutely would insulate and air tighten my suspended floors but mightn't want to loose their character so how to do it would be open to debate.

3. I would ensure that appropriate ventilation is designed in early and perhaps included with that of the new build extension. A 1920's house suggests a number of chimneys. Chimneys are also known as passive stack ventilators. What are the plans for these?

4. I would finally decide on my heating source and distribution system when I would have a far better understanding of what both my heat demand and heat load are likely to be. I would try to match the source with the distribution system (for example, low temperature source (hp) with low temperature distribution system (uf) etc) as well as taking some practical aspects into account such as who do I call in the future when (not if) my system develops a fault in the depths of winter and I need it sorted asap.

New extension:

Build passive. Simples
 
Thanks a mill @Micks'r for such a brilliant/detailed answer.

This is all really valuable when we sit down with architect to ask him (slightly) informed questions to make sure all things airtightness, ventillation, insulation, heating are considered and thought through. Current planned architect is very bright, not certain how good he is on specifications for insulation, ventilation & airtightness - we just haven't got into the detail on this, but I have seen his drawing packs for builders and they are very detailed. If he doesn't want to get into the detail on this I can always get additional professional(s) to advise.

Re airtightness - I understand the importance....though until now I had kind of been ignoring a scientific approach as am conscious that chimneys & front door with single pane stained glass side panels and window does not play well with low air tightness scores. Herself is not keen on a porch to the front door so this is a challenge re airtightness.

I figured doing the floors, good windows, attic etc makes it much better, and was going to leave it there. But I take your point that being able to answer questions on heating is dependent on the approach to airtightness, amongst other things.

Re chimneys....we'll probably end up with only one "in use" fireplace. The other chimney downstairs will become a stove, to be confirmed. Other chimneys are in 3 bedrooms, currently covered over (metal plate in fireplace opening to chimney).

I'm also quite concerned about thermal bridging and overall decisions on insulation in relation to this, as you have alluded to. We have solid concrete soffits/fascias, so that adds complexity I believe. We dont have any insulation on walls, internal or external. We also have "hip roof" I think it is called, another complexity. I figure by converting the attic, as well as gaining valuable space, we also gain by dealing with any airtightness/insulation that needs to be addressed.

I'm not 100% sure what you mean re build passive for the extension - the extension is largely half of an open plan kitchen/utility area, the other half being one of the current reception rooms.
 
Take a look at this guide, it provides decent guidance on what should be tackled first in terms of return on investment for a lot of the common Irish house types.
That's a great document, thank you for the link Leo. Though I just find it hard to actually believe that adding 100mm external insulation to 2 ft thick stone walls is actually going to do any good on a "Type 1" house like ours...
 
That's a great document, thank you for the link Leo. Though I just find it hard to actually believe that adding 100mm external insulation to 2 ft thick stone walls is actually going to do any good on a "Type 1" house like ours...
I've talked with with a well versed conservation joiner on this who is in and out of many building like this. You've to be very careful when dry lining or insulating stone walls. The walls are designed to breathe so need to do so or damp and mould issues can result.
 
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