Continue passive retrofit or knock down and rebuild as passive house..

[rsimon]

Hi all,

We've been slowly doing a retrofit over the past two years or so with the aim to get Enerphit certification. We have done a PHPP with the help of a passive house designer. Current status is this: half of the windows and the front door have been replaced with passive certified components. We have an MVHR installed (hard work retrofitting this, but it is in). We've just put in a new kitchen, done three bathrooms. We plan to rebuild the upstairs, replace the rest of the windows, replace the roof with insulation etc. We will certainly struggle with air-tightness. While doing all this, I am now wondering if it makes sense to continue this further, or knock down the house and rebuild from scratch as a fully certified passive house, perhaps using ICF for speed of construction. I'm trying to build a business case for this with the following approach:

 

- We use the current windows and front door in the new plan.
- We use most of the components in the three bathrooms we have just done up including shower trays, glass partitions, toilets, furniture etc.
- We use the new kitchen and appliances we have just put in.
- We use the MVHR unit but redo the ducts in the new house.
- We save money with reduced energy bills over say 15 years, compared to the current house or even become net zero positive with solar.
- We are planning to rebuild the upstairs anyway as per the current plan with a new insulated roof and replace the rest of the windows in the house. So is it just the new foundations and the ground floor structure and finishings that'll be extra?

 

With the above approach, does it make sense to think about a knock down a rebuild, which will give us a better house without the retrofit related compromises? Obviously there will be costs associated with demolition etc. I'm not sure how to begin analysing this. Has anyone done anything like this or can provide some useful nuggets to ponder? Any thoughts will be much appreciated. Thank you.

[Gus Potter]

19 minutes ago, rsimon said:

We've been slowly doing a retrofit over the past two years or so with the aim to get Enerphit certification.

Hat off to you for giving Enerphit a go.

 

Here is a question. Is it important to you that you reduce your carbon foot print and overall footprint on this earth during your life span?

 

It's a serious question as you clearly know your ins and outs if you have been exploring Enerphit.

 

For me.. a bit of a philstine I have an ex council house that I am insulating as much as I can, experimenting with eco stuff.. but recognise that if I demolished it then the real carbon footprint would be prohibitive unless I put a life cycle of 200 years on the house at least.

 

Stuff like planning fees.. I can get a lot of insulation for that!

 

Keep us posted on your thoughts.

 

 

 

 

 

[ToughButterCup]

Have a read of @VIPMan's posts...

[Dave Jones]

on the plus side you would get all the VAT back and end up with a much better built house. 

 

Do you plan on staying there for a long time ?

[joth]

Yes well done on what you have achieved so far.

We did an enerphit (certified), but did it in one big hit rather than piecemeal. So here's my experience and thoughts.

Financially ours was borderline (mostly due to the VAT saving if we'd rebuilt) but the process would have taken longer (probably another 2 years in planning alone, based on average for modern rebuilds I know in our area) and we wanted to live in the completed house, not the wreck we had bought, which was the real decider. Plus of course the lifetime CO2 savings of retrofitting. We never worried about hitting airtightness as we were paying an experienced team to do it all in one go (achieved 0.5ach 👌).

For you it seems you're living in it while DIYing the work. So the time and logistical hit to go to a rebuild will be bigger as you'll have to move out for a year+ (more if you plan to slow build it yourself). How many in the house and how will they all handle that disturbance to their lives? And you have to find somewhere secure to store all the components you'd like to reusue.

 

If it's just the risk on airtightness giving you doubts then consider how much you need the certification. "Good enough" airtightness may well be good enough even if you miss the goal. Play in PHPP and see what happens if it's 1.5 or 2.

I'd only think of rebuilding if it's what I was emotionally heart set on. Not just because one box may not be ticked on the approach you're already on. 

There's absolutely no question the rebuild can be better quality outcome. Unfortunately you've undermined several of VAT savings by reusing MVHR, windows, kitchens and bathrooms. The VAT on those often helps swing the decision. Instead you'll be paying VAT on storing them for a couple years 

 

Edited May 19, 2023 by joth

[ProDave]

Think of the logistics of moving out and storing all that stuff you plan to re use, without damaging it.  If you have a handy barn, fine, but if you have to rent storage factor in the costs of that, and transport, properly.

 

If you carry on, air tightness seems to be the issue that is concerning you.  I assume enerphit has an air tightness requirement like passivehause does?  Would it really be a "fail" if you did not meet the air tightness requirement so failed to get enerphit, but still had a warm cheap to run low energy house?  There are many on here like myself that just aimed for a low energy house without any certification, the constantly warm house with low heating bills was all we wanted.

[JohnMo]

Really - you have put 2 years into it and now you want to knock it down and build from scratch. By the time you get planning and built another 2 years, if you get contractors in, 3 or more if you do lots yourself.

 

How much heating energy do you think you will save to recover costs. So build cost £2k/m2, 100m2, is £200k to build, save £1k a year on heating (which you won't)- 200 years pay back. 

 

Get some decent contractors in and get it done. Money obviously not an issue, or you wouldn't be posting the question.

 

Or is getting a passivhaus badge the important bit?

[Iceverge]

7 hours ago, rsimon said:

replace the roof with insulation etc. We will certainly struggle with air-tightness.

 

This is the rescue for me. 

 

Airtightness won't be an issue if you do it externally to the current skin of the house before EWI with a parge coat or membrane or paint on sealer. 

 

You can likewise build the new roof as a hybrid/warm roof and use a ply/OSB layer fully taped as your airtight layer. External airtightness is more straight forward than internal anyway. 

 

Given the roof hasn't been done extend it to give as much of an overhang as possible and you can then have enough insulation to make the build a passivhaus too. 

 

 

Edited May 19, 2023 by Iceverge

[Iceverge]

https://passivehouseplus.ie/news/marketplace/passive-purple-used-to-seal-beattie-passive-enerphit

 

Here's an example of an Enerphit where they did just that. 

 

[MikeGrahamT21]

To me it sounds like your already way past the point of no return given the amount of money you'll have spent, not to mention the effort. I'd carry on as you are

[rsimon]

Hi @Gus Potter, thanks for the comment. Reducing carbon foot print is important to us and at the moment we're only simply thinking in terms of enhanced comfort not just for us but also for anyone living in the property in future. Also doing our bit for the environment for the next gen. I feel that if we do piecemeal, it will put us in a position of not really knowing if it's made any real difference at all. This is one of the reasons for choosing to do Enerphit both in terms of methodically approaching it and also having a standard to meet that we can use to measurable value added.

 

Hi @ToughButterCup, will check it out, thanks.

 

Hi @Dave Jones, yes, VAT is certainly one of the considerations. And we do hope to stay here for a while.

 

Hi @joth, thanks for the comments and for sharing your experience. We did start off with the intention of doing it in one go but due to some reasons out of our control had to phase it. Airtightness is a key consideration for us primarily in order to get good air quality for health reasons. We did a lot of intrusive work before moving in but appreciate that we have to move out for some time at some point with either option. Four in the family with two kids, and I don't think they would mind the adventure of moving out for a few months if it is guaranteed that they'll come back to a better house. There is an emotional aspect to this as well as there are some retrofit compromises due to the nature of the house which we can potentially get rid of when starting from a clean slate. I do get the very valid point around VAT!

 

Hi @ProDave, Yes, Enerphit specifies 1.0 ACH@50Pa. If we fail the air-tightness test it would be a mental fail/disappointment, but won't have a choice but move on at that point I guess. Badge would be great to have though. And I don't think energy savings alone will pay for any of this. At least not in our lifetime. One of my frustrations is contractors, especially for retrofitting to a standard. No one I have come across has any clue on what I am taking about and always try to convince me that it's a waste of time. Really tired with that process and also do not have the time to be around all the time to track quality of work. I don't know if this is a general problem. At least with a new build I can hand this over to a specialist and step back.

 

Hi @Iceverge, our current air-tightness approach is external with a parge coat (using the EWI adhesive) as you have rightly suggested, but the purple paint is an interesting option. I'll certainly check it out. Another frustration is that our current approach specifies that we fill the cavities to really guarantee airtightness and I found out recently that there is batt insulation in some of the walls which requires specialists to get it out. I'm not sure if this is a must if the purple paint is used. Do empty cavities contribute to air leakage? The roof is also going to be warm with the approach you have mentioned with an airtight OSB deck.

 

Hi @MikeGrahamT21, thanks for the observation and input. Very valid indeed. I've heard the same from some family members as well but however mad the idea is, I just want to do a proper comparison and assessment and then discount the idea if it doesn't make sense.

[BadgerBadger]

It sounds like the measures you're implementing already have got you a good, comfortable house.

 

Yes there are more things you could do if it was a new build, but if reducing your overall footprint is the driving motivation then knocking down a perfectly livable house doesn't feel very environmentally conscious.

 

By all means investigate further just don't forget to take the whole lifecycle impact into account when weighing up your options, not just the resulting energy usage of the completed house.

[Sparrowhawk]

6 hours ago, rsimon said:

One of my frustrations is contractors, especially for retrofitting to a standard. No one I have come across has any clue on what I am taking about and always try to convince me that it's a waste of time. Really tired with that process and also do not have the time to be around all the time to track quality of work. I don't know if this is a general problem.

 

It is. I'm more jaded than usual at the moment trying to organise work, and experiencing everything you have said and more. I get that people are running businesses but the base work is shoddy before even getting to the lack of attention to detail or insulation. My FIL is dealing with a commercial project atm where the construction company cut lintels short and packed with mortar, didn't pack under the pads (more large mortar chunks), mounted steels onto the current unreinforced concrete floor without a foundation, and a new wall was built bowing from the start. They overcharged by 50% which doesn't bother me (it's business) but doing a crap job... that's wrong.

 

6 hours ago, rsimon said:

At least with a new build I can hand this over to a specialist and step back.

You hope. There's a fair few horror stories on this forum of what the contractors for specialists get up to...

[ProDave]

7 hours ago, rsimon said:

Hi @ProDave, Yes, Enerphit specifies 1.0 ACH@50Pa. If we fail the air-tightness test it would be a mental fail/disappointment, but won't have a choice but move on at that point I guess. Badge would be great to have though. And I don't think energy savings alone will pay for any of this. At least not in our lifetime. One of my frustrations is contractors, especially for retrofitting to a standard. No one I have come across has any clue on what I am taking about and always try to convince me that it's a waste of time. Really tired with that process and also do not have the time to be around all the time to track quality of work. I don't know if this is a general problem. At least with a new build I can hand this over to a specialist and step back.

If it is any consolation, I was disappointed my air test came in at 1.4, though the tester was having kittens saying it was the best one he had yet tested.  The building still performs very well, heating usage is exactly in line with what the heat loss calculation says it should be.  There are no noticeable draughts and it fits my basic test that on a windy day you can open 1 window or 1 door with no perceivable draught entering or leaving that one open door or window. (previous house with all the plethora of individual extract fans, window trickle vents, cat flat, letter box etc, if you did that there would be a draught blow through and likely an internal door blow open or shut)

 

So although it would have been a "fail" that does not mean it is a bad building and was a waste of time trying or it is going to waste a lot of energy.

 

The flaw in your argument is if you knock down and rebuild you would just employ a specialist to do it all properly.  I only know of one timber frame company that will erect a complete frame and guarantee a particular air tightness figure.  And that is for the bare shell.  You then have to guarantee that all your following trades, plumbers, electricians, even joiners, do not drill holes in your air tightness layer and destroy your good air test.

 

It is a sad reflection on the UK building trade that most tradesmen in the industry don't have a clue about air tightness and think you are being silly when you talk about things like that. 

 

You really are best seeing to the detail yourself, you have done a large part of the house already, just carry on.  With a rebuild I bet you would either still be doing the detail yourself, or complaining that it has been done wrong and having that same argument.

[Iceverge]

9 hours ago, rsimon said:

our current air-tightness approach is external with a parge coat (using the EWI adhesive) as you have rightly suggested, but the purple paint is an interesting option. I'll certainly check it out. Another frustration is that our current approach specifies that we fill the cavities to really guarantee airtightness and I found out recently that there is batt insulation in some of the walls which requires specialists to get it out. I'm not sure if this is a must if the purple paint is used. Do empty cavities contribute to air leakage? The roof is also going to be warm with the approach you have mentioned with an airtight OSB deck.

 

Normally if you were to retrofit cavity wall insulation like EPS blown beads or mineral wool then the supplier would insist on removing the existing cavity wall insulation to be able to guarantee against water ingress. However in the situation where you have EWI they should be happy to just top up the existing. 

 

Do you have any pics of the house as is? It must be relatively modern if there's mineral wool batts already in the cavity. 

 

Airtighess and insulation are separate things entirely unless you use something like closed cell foam or open cell foam/cellulose in a timber frame. 

 

Any pics/cross sections drawings of the house would help. 

 

Is it detached? What kind of roof do you have? How sticky are the authorities about external alterations? 

 

[joth]

On 21/05/2023 at 11:07, Iceverge said:

 

Normally if you were to retrofit cavity wall insulation like EPS blown beads or mineral wool then the supplier would insist on removing the existing cavity wall insulation to be able to guarantee against water ingress. However in the situation where you have EWI they should be happy to just top up the existing. 

 

Do you have any pics of the house as is? It must be relatively modern if there's mineral wool batts already in the cavity. 

 

Airtighess and insulation are separate things entirely unless you use something like closed cell foam or open cell foam/cellulose in a timber frame. 

 

Any pics/cross sections drawings of the house would help. 

 

Is it detached? What kind of roof do you have? How sticky are the authorities about external alterations? 

 

Cavity walls are a nightmare for airtightness. This is why we put airtight layer on the inside of our retrofit walls. If doing external airtightness retrofit over a cavity wall, I think filling the cavity with a airtight foam (that happens to also be an insulator) is the best hope. Else the air can enter the cavity anywhere at all internally and work down through and under the foundations. In fact seen this happen on another retrofits even though they used internal airtight layer. 

 

How expensive a specialist are you talking to remove batt insulation? Demolishing the entire house to remove it sounds a fairly extreme alternative.

 

Edited May 22, 2023 by joth

[rsimon]

On 21/05/2023 at 11:07, Iceverge said:

 

Normally if you were to retrofit cavity wall insulation like EPS blown beads or mineral wool then the supplier would insist on removing the existing cavity wall insulation to be able to guarantee against water ingress. However in the situation where you have EWI they should be happy to just top up the existing. 

 

Do you have any pics of the house as is? It must be relatively modern if there's mineral wool batts already in the cavity. 

 

Airtighess and insulation are separate things entirely unless you use something like closed cell foam or open cell foam/cellulose in a timber frame. 

 

Any pics/cross sections drawings of the house would help. 

 

Is it detached? What kind of roof do you have? How sticky are the authorities about external alterations? 

 

We are thinking of using an a liquid foam that they pour into the cavities that slowly expands to fill the cavities. Hence the steps to try and remove the batt insulation. Its a detached house, was a bungalow built in the 60s, but gradually extended on either side over time, as recent as the early 2000s so not has most of the cavity walls empty except the newer side where there is batt insulation. The PH consultant has said that we need to fill the cavity first (for airtightness) then do EWI. The roof is a standard timber joist roof, concrete tiles (!?). We have planning and within it we have mentioned EWI etc. Local authority is happy.

[MikeGrahamT21]

1 minute ago, rsimon said:

We are thinking of using an a liquid foam that they pour into the cavities that slowly expands to fill the cavities. Hence the steps to try and remove the batt insulation. Its a detached house, was a bungalow built in the 60s, but gradually extended on either side over time, as recent as the early 2000s so not has most of the cavity walls empty except the newer side where there is batt insulation. The PH consultant has said that we need to fill the cavity first (for airtightness) then do EWI. The roof is a standard timber joist roof, concrete tiles (!?). We have planning and within it we have mentioned EWI etc. Local authority is happy.

 

If you use liquid foam in the cavity, you will be limited to breathable only products on the external insulation, wood fibre, rockwool etc, you won't be able to use EPS or Phenolic, something to bear in mind

[rsimon]

On 22/05/2023 at 13:43, joth said:

Cavity walls are a nightmare for airtightness. This is why we put airtight layer on the inside of our retrofit walls. If doing external airtightness retrofit over a cavity wall, I think filling the cavity with a airtight foam (that happens to also be an insulator) is the best hope. Else the air can enter the cavity anywhere at all internally and work down through and under the foundations. In fact seen this happen on another retrofits even though they used internal airtight layer. 

 

How expensive a specialist are you talking to remove batt insulation? Demolishing the entire house to remove it sounds a fairly extreme alternative.

 

Hi @joth yes agree, hence the approach mentioned above. Although I still worry about a couple of internal walls that used to be external and hence have cavities. No way we can fill these! The firm that came and had a look at the insulation removal has quoted just over £5k for it. Filling all cavities with the liquid foam comes to around £8k.

[rsimon]

1 minute ago, MikeGrahamT21 said:

 

If you use liquid foam in the cavity, you will be limited to breathable only products on the external insulation, wood fibre, rockwool etc, you won't be able to use EPS or Phenolic, something to bear in mind

Oh! I wasn't aware of that. The foam itself is closed cell and not breathable isn't it?

[MikeGrahamT21]

Just now, rsimon said:

Oh! I wasn't aware of that. The foam itself is closed cell and not breathable isn't it?

 

It is indeed yes: https://walltite.basf.co.uk/

[Plumsnson]

How are you getting on?

Did you go with the advice here about topping up cavity insulation and creating your airtight later elsewhere?

It sounded like the plan proposed to you by contractors and your consultant needed challenging.

 

Hope it is going well!