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Extending a Victorian Farmhouse


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Hi everyone,

 

I've been stalking the forum for quite a while after buying a farmhouse in Nantwich to renovate and thought I should finally introduce myself.

 

I'm an engineer who has taken 6 months out of work to work with my builder to the majority of the build done. We have put nin steels and are putting in the slab next week so are on with the build but some of the finer details will need ironing out as I get to them.

 

I'm almost doubling the size and the inside has been gutted and insulated so it can be brought up to a modern standard. I'm not aiming for a passive house but am putting in a fair amount of insulation, MVHR, ASHP, rainwater tanks etc. 

 

I have a few questions which I'll put int he relevant sections for some help.

 

I really like the forum because it contains a wealth of information and on occasion differing opinions which is something I like as I can choose which one I agree with :)

 

Here are a few pictures so you can see the project,

 

Frank

 

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The original house was build in 1897 I think - We have found the original plans which are drawn on cloth.

 

We are planning on framing them alongside the new ones if we every get to that point!

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On 28/04/2022 at 21:12, FrankHouse said:

We are planning on framing them alongside the new ones if we every get to that point!

I was going to suggest they should be displayed. What a great find. 

 

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3 hours ago, DevonKim said:

That's a really attractive farmhouse, isn't it?  What are you planning to do to it?  

Thanks, i swing back and forwards between admiring the different bits and then disliking the asymetry... but overall I like it.

 

it was a t shaped building with two large front rooms and a small kitchen dinning room, scullery at the back.

 

we are squaring it off and adding a modern looking section to the rear with the usual big open kitchen diner. Inside the old bit, it's back to brick to try and make it affordable in the era of high energy prices, so pir insulation, ufh, ashp, mvhr... all the acronyms you can think of. I'll put up pictures as I move through the build.

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On 02/05/2022 at 20:49, Iceverge said:

 

Have you had any vapour flow analysis for the walls done? 

 

 

 

I had to Google what that was am still none the wiser to be honest.

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https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1019707/iwi-guidance.pdf

 

 

Worth a read. Using a non breathable material on as internal wall insulation (IWI) like PIR comes with risks, especially on heritage structures. Interstitial condensation, thermal bypass and structural decay are some. 

 

It's been discussed at length on here already. Search IWI for more reading. 

 

I'm of the camp that would prefer a breathable ( vapour open ) internal wall insulation like

--woodfiber and lime plaster or

--rockwool batts and a humidity variable membrane like proclima intello plus. 

 

Others are happy with PIR etc but this relies on a perfect vapour membrane internal to the insulation which is almost impossible to achieve with a retrofit. 

 

 

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29 minutes ago, Iceverge said:

https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/1019707/iwi-guidance.pdf

 

 

Worth a read. Using a non breathable material on as internal wall insulation (IWI) like PIR comes with risks, especially on heritage structures. Interstitial condensation, thermal bypass and structural decay are some. 

 

It's been discussed at length on here already. Search IWI for more reading. 

 

I'm of the camp that would prefer a breathable ( vapour open ) internal wall insulation like

--woodfiber and lime plaster or

--rockwool batts and a humidity variable membrane like proclima intello plus. 

 

Others are happy with PIR etc but this relies on a perfect vapour membrane internal to the insulation which is almost impossible to achieve with a retrofit. 

 

 

 

I'm leaning towards the other camp. Mainly because going down the breathable route 1) further decreases floor space and 2) forever limits you to breathable finishes (lime plaster, breathable paints, non-vinyl wallpapers etc).

I'd love to have an informed conversation about this though, as I hope to make a start on ours towards the end of summer, ready for winter. My current opinion is;

  • breathable IWI is preferable
  • non-breathable is acceptable, but
    • great care needs to be given to the VCL detailing
    • there's a limit to how well you should insulate to allow some heat still to escape and help dissipate any moisture in the wall - so forget PassivHaus levels, Enerphit propose a u-value of 0.35 when using IWI which is higher than building regs now require of a renovation, so I don't know how that works. 
    • the external face of the wall must be breathable - no cement render, well pointed with lime mortar, no ground build up etc.
      • some suggestion that a water repellent should be applied to the external face to reduce the risk of moisture ingress. 

If I was to go the breathable route, I'd probably use this - https://www.ecologicalbuildingsystems.com/product/diathonite-evolution - to provide the insulation and airtight layer all in one.

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We could really do with some proper controlled studies on this using real life builders and projects.

 

The academic studies don't tend to allow for various levels of workmanship, waste, cost, time and availability of materials. 

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Posted (edited)
19 minutes ago, Iceverge said:

We could really do with some proper controlled studies on this using real life builders and projects.

 

The academic studies don't tend to allow for various levels of workmanship, waste, cost, time and availability of materials. 

 

Agreed, you hinted at something interesting. If I was to get someone in to do this work, they'd probably slap 75mm PIR everywhere, batten out, PB and be on their merry way.

 

Whereas home owners generally take more care and attention in work they DIY. I'd be more tempted to apply 2x layers of 25mm PIR taped and overlapping each other, an additional VCL, batten out, 25mm PIR infill (taped) and then PB. So you could certainly see which one would be more likely to incur interstitial condensation.

 

I'm even considered rigging up some Temp + Humidity sensors behind the PIR, to see what really happens during the coldest/wettest months.

Edited by jayc89
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I have read around the subject and all of the posts on this forum I could find so am aware of the two camps.

 

I'm in the camp that hopes doing it myself and taking care will result in a workable outcome. But I also acknowledge that its a risk, but at least its my risk.

 

I put a post in the heat insulation section to discuss what other mitigation I can put in but haven't seen any replies yet.

 

As you say its very anecdotal at the moment and the academic work is lacking.

 

I'd have thought there would be loads of people on here with iwi pir that works as they installed it years ago?

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I renovated a Victorian farmhouse! I went with wood fibre - didn't much fancy degassing PIR and there were issues in the house where foil backed plasterboard had been used (literal water dripping off the back of it when removed). I also didn't do a complete gutting of the house so I knew I'd never get a complete VCL, but I did put in MVHR, a ASHP (new CH - well, there wasn't one before) and an extension..

 

For interstitial condensation, if you have MVHR and you're able to put in a decent VCL then you would think the risk is much reduced. 

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11 hours ago, George said:

I renovated a Victorian farmhouse! I went with wood fibre - didn't much fancy degassing PIR and there were issues in the house where foil backed plasterboard had been used (literal water dripping off the back of it when removed). I also didn't do a complete gutting of the house so I knew I'd never get a complete VCL, but I did put in MVHR, a ASHP (new CH - well, there wasn't one before) and an extension..

 

For interstitial condensation, if you have MVHR and you're able to put in a decent VCL then you would think the risk is much reduced. 

 

I'd love to know more about this. Was the source of the moisture ever discovered? What was on the external face of this wall; any render? was it well pointed with lime? any damaged guttering etc?

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7 hours ago, jayc89 said:

 

I'd love to know more about this. Was the source of the moisture ever discovered? What was on the external face of this wall; any render? was it well pointed with lime? any damaged guttering etc?

It was actually an internal wall but was into a boot room/porch which is unheated so effectively like an external wall but without the driving rain.

 

So the source was condensation. Water vapour is everywhere but if it hits a cold surface below the dew point it'll condense. So the foil backed plasterboard (dry lined over gypsum) wasn't allowing water vapour to disperse so the humidity went up and up until the dew point was room temperature (with no CH, room temperature was pretty low). 

 

Ripped it off an replastered in lime. I've got some salts crystallising on the surface now but is dry and warmer for it. Assuming the salts are from the gypsum so just vacuum them up and I'll repaint in a few years. 

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16 minutes ago, George said:

It was actually an internal wall but was into a boot room/porch which is unheated so effectively like an external wall but without the driving rain.

 

So the source was condensation. Water vapour is everywhere but if it hits a cold surface below the dew point it'll condense. So the foil backed plasterboard (dry lined over gypsum) wasn't allowing water vapour to disperse so the humidity went up and up until the dew point was room temperature (with no CH, room temperature was pretty low). 

 

Ripped it off an replastered in lime. I've got some salts crystallising on the surface now but is dry and warmer for it. Assuming the salts are from the gypsum so just vacuum them up and I'll repaint in a few years. 

 

So it could be said that it was caused by poor detailing. If a VCL was in place to prevent moisture reaching the cold wall, that condensation would have not happened?

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15 hours ago, jayc89 said:

 

So it could be said that it was caused by poor detailing. If a VCL was in place to prevent moisture reaching the cold wall, that condensation would have not happened?

The foil backing was the vcl. For me it showed the issues trying to retrofit a vcl to an old building. If a building is completely stripped back then it may be possible, but for me, vapour permeable options are more forgiving with no real failure mode. 

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1 hour ago, George said:

The foil backing was the vcl. For me it showed the issues trying to retrofit a vcl to an old building. If a building is completely stripped back then it may be possible, but for me, vapour permeable options are more forgiving with no real failure mode. 

 

My assumption is that because the VCL was on the rear of the plasterboard so couldn't be made continuous, whereas PIR taped, followed by plasterboard, or a separate VCL entirely would have been more suitable.

 

Totally agree that breathable is more failsafe though!

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4 hours ago, jayc89 said:

 

My assumption is that because the VCL was on the rear of the plasterboard so couldn't be made continuous, whereas PIR taped, followed by plasterboard, or a separate VCL entirely would have been more suitable.

 

Totally agree that breathable is more failsafe though!

is breathable more forgiving?

 

Doesn't this mean that you will definitely get moisture throughout the structure so won't the walls be wetter? I'm not sure if that's a problem or not...

 

I understand that moisture can evaporate from both sides but there will be a moisture gradient through the wall is my assumption. the difference is that it won't be all at one point so it would look different and would all be in one place (as you have seen) but surely the same moisture is there?

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