Enerphit (Passivhaus retro-fit)

  • 14 January 2020
  • 6 replies
  • 374 views

Is anyone interested in a DIY project I've done to convert a standard bungalow into a Passivhaus retro-fit?
The house:
- 3 bedrooms;
- South facing, west coast of Scottish Highlands;
- Rendered blockwork exterior;
- Timber frame interior.
Conversion:
- Strip out all internal walls, floors, ceilings;
Walls
- build new internal 'skin' 300mm rockwool;
- 9mm board with airtight Tyvek membrane;
- 25mm service gap:
- plasterboard.
Floor
- 400mm supported rockwool;
- Tyvek airtight membrane;
- reconditioned t&g flooring.
Ceiling
- 450mm rockwool;
- 9mm board with airtight Tyvek membrane;
- 25mm service gap;
- plasterboard.
Glazing
- S-facing windows now floor-to-ceiling triple-glazed. All other windows triple-glazed.
Ventilation
- all rooms ducted;
- Pauls 94% efficient heat recovery system;
Heating
- fully enclosed external air 4 kWh wood stove
Cooking
- induction hob, A-rated oven
Lighting
- LED throughout.
Hot Water
- solar vaccuum tube system with immersion top-up.

Free advice, pictures etc to anyone interested.

6 replies

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hi Energyphit,
great post and I'm sure there will be lots of interest and questions, you can post photos and details on here if you wish.
I just looked up the Pauls heat recovery.
A wood stove isn't very environmentally friendly (not judging just saying), and tell us about the solar vacuum system? I've not heard of those.
Interesting username - do you work in the energy effeciency improvement sector?
I'm considering triple glazing as need some frames replacing, are there any snags? What's the air gap in each, is it the same? Are the units very expensive compared to double?

Energyphit;46312:
Is anyone interested in a DIY project I've done to convert a standard bungalow into a Passivhaus retro-fit?
The house:
- 3 bedrooms;
- South facing, west coast of Scottish Highlands;
- Rendered blockwork exterior;
- Timber frame interior.
Conversion:
- Strip out all internal walls, floors, ceilings;
Walls
- build new internal 'skin' 300mm rockwool;
- 9mm board with airtight Tyvek membrane;
- 25mm service gap:
- plasterboard.
Floor
- 400mm supported rockwool;
- Tyvek airtight membrane;
- reconditioned t&g flooring.
Ceiling
- 450mm rockwool;
- 9mm board with airtight Tyvek membrane;
- 25mm service gap;
- plasterboard.
Glazing
- S-facing windows now floor-to-ceiling triple-glazed. All other windows triple-glazed.
Ventilation
- all rooms ducted;
- Pauls 94% efficient heat recovery system;
Heating
- fully enclosed external air 4 kWh wood stove
Cooking
- induction hob, A-rated oven
Lighting
- LED throughout.
Hot Water
- solar vaccuum tube system with immersion top-up.

Free advice, pictures etc to anyone interested.
The wood stove is the best option where we are as we have 20+ mature trees in the garden. The stove, a 'Westfire One MF', claims 80% efficient burning.
Last night storm Brendan was in full song. Outside air temp was 2-4deg.C.
We lit the fire at about 6:30pm because the temperature had dropped to 19deg C. by 9pm the house (whole house) was at 24deg.C.
We used 6 chunky logs.
That's warm enough for us. By 10am today the temperature was down to 20deg.C. That will go down to about 19deg.C by 6pm and the cycle will start again. On a sunny winter day we can sometimes manage without any supplementary heat because of solar gain through the large windows.
The ventilation unit is 'Zehnder ComfoAir Q 350'. It is a fairly expensive option but a building regs requirement because of the wood stove. The reason is that this unit monitors internal and external air pressure and has 2 motors (supply and extract) to always guarantee positive air pressure inside the house. If the stove is opened the system cannot suck in smoke/carbon monoxide. If we had used a non-combustion heat source we could have opted for an equally efficient but cheaper model with a single motor.
Triple glazing is a luxury. I can sit on the floor beside the full-height window with snow outside and there is no down-draught. The very best spec double-glazing is only slightly less effective than passivhaus spec triple-glazing and it is somewhat cheaper (but you will get a down-draught). If you are doing it yourself you feel you might as well go for the ultimate.
Solar hot water using vacuum tube collectors: The collectors are long glass vacuum tubes with the actual heat collection inside the vacuum ... thus being completely insulated from external air temperature. Heat is transferred at the top of each tube to a circulating system connected to the HW tank. Although slightly more expensive it is a more effective system in a cold Northern area as flat collectors are more affected by external air temperature.
We use about 5000kWh per year and if we stopped using the tumble-drier that would go down considerably.
I'm not a professional energy consultant!. I have done a lot of research, bought the PHPP (Passivhaus Planning Package), visited Passivhaus homes and worked on a few projects involving those pronciples. My home is not Passivhaus certified and I won't bother with certification unless I have to sell it ... but I'm confident it would reach the retro-fit standard for Passivhaus.
Passivhaus spec is extremely high; on a retrofit there are concessions to allow for the existing building, difficulties in thermal bridging, airtightness etc. Passivhaus is not just about energy use, it is about a healthy living environment. Mechanical ventilation does three main jobs:
- constantly refreshes the air,
- recovers heat from exhaust air,
- moderates smells, condensation, humidity.

My thoughts on triple-glazing vs double-glazing: (Passivhaus: U-value of 0.85W/m2K installed - includes performance of frame etc.). I don't think any UK manufacturer meets this standard so it means importing the windows. Also the method of mounting the units in relation to the insulated wall is tightly specified.
Is replacing double-glazed with triple-glazed worth it? If your budget is tight the highest spec double-glazed, argon filled, large gap (up to 16mm) with high-spec insulated frames will be cheaper than triple-glazed windows that meet the Passivhaus standard.
If you have a house where the heat source is low level such as under-floor or radiators and the windows aren't at floor level the down draught issue and triple-glazing is not worth worrying about. But that's just my opinion.
Hi @Energyphit
Welcome to the community!
This is a great post, really interesting.
It would be great to see some pics, if you're happy to share a few.
(It's a good idea to add photos one at a time, ie a new reply for each pic. Only because sometimes adding multiple photos to one post can crash your web browser, which is v annoying!)
BTW I've moved this great post to our 'renewables' section and pinned it at the top. 👍

Thanks for all the info @Energyphit exactly what I was looking for!  We're about to embark on a new-build and (obviously) want it to be as energy-efficient as possible.  I'm not sure we'll go full PH spec, but can you point me in the right direction to begin general  research and self-education? Are there any PH spec buildings that can be visited locally (Bath)?

Hi,

It is really useful to experience a passivhaus. I went to 3 open days before starting on my project.

You can find out about them at:

https://www.passivhaustrust.org.uk/event_detail.php?eId=627#South%20West

This year the open days are 6-8 November. There will be some in the Bath area - published nearer the time. You can also look at the properties that were ‘open’ in 2019 on the same site.

Talking to someone who ‘lives it’ gave me an insight. The literature focuses on the low energy requirement but if you ‘live’ passivhaus the most important thing is comfort and health.

I cannot over-emphasise the difference that mechanical ventilation and heat recovery (MVHR) makes to the interior environment. It stays fresh and the ambient temperature is much more stable regardless of weather. Even when it is cold and we haven’t bothered to add heat there are no cold zones or drafts and the temperature doesn’t drop sharply. It is particularly noticeable in extreme weather. We have had a few violent storms up on the West coast of Scotland and we can look out on thrashing trees and lashing sleet and yet the interior feels calm and comfortable. Our neighbours are hunkering down and feeding their fires and complaining. It’s difficult not to be smug.

As for trying to achieve the full PH spec … as a retrofit we obviously couldn’t quite make it. Here are some of the areas where we failed:

  • The windows to the North are too large. They are triple-galzed to ph spec but basically they allow too much heat loss (but there is quite a nice view of the wood).
  • The back door is ony double-glazed as a triple-glazed door would have meant some major masonry adjustments which didn’t seem worth it.
  • the fireplace and chimney still introduce some thermal bridging although I’ve minimised it - a new build could eliminate that.

I suppose it  depends if you want to have it certified. I haven’t bothered with certification as I don’t intend moving. If I was forced to move (health say) I would try to have it certified.

Have you got the PHPP? It is essential if you are doing most of the work yourself. Even if someone else is doing the work it gives you an insight into the fine detail required and the rigour needed to make the house ‘function’.

I need to make time to do a youtube video of what I did. Time! Time!

 

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