Guy Martin’s House Without Bills

[sgt_woulds]

3 hours ago, Nickfromwales said:

If moisture was routinely buffered any further into the fabric of a domestic residence, that’s just too far and has not been addressed or controlled properly.

 

Seasonally, perhaps this is an acceptable swing, but day to day it should be the immediate room interior surfaces at most.

 

I dislike this approach, and am not afraid to say it!

 

Grab the heat and moisture, use it to better facilitate heat recovery, and get the MVHR in and running.

 

Tin hat time. 

 

 

Restricting moisture sorbing and release to the surface materials (Gypsum plaster boards) limits the positive benefits of stable indoor moisture levels that natural insulations can provide.  Not an issue with MVHR of course (unless there is a sustained power cut in winter with high occupancy) as this is artificially removed.

 

Personally, I'd rather not rely on a mechanical system to stay healthy indoors.  Horses for courses.  And I prefer my straw hat to tin foil 🙂 

[JohnMo]

11 minutes ago, sgt_woulds said:

Personally, I'd rather not rely on a mechanical system to stay healthy indoors.

I've done both, woodcrete ICF is a good hydrophilic material I believe, but good airtightness and MVHR to capture any ventilation heat losses.

[Nickfromwales]

1 hour ago, sgt_woulds said:

I'd rather not rely on a mechanical system to stay healthy indoors

So no mechanical fans in kitchen / utility / bathrooms etc?

[sgt_woulds]

With iPSV you don't need a fan in the bathroom or kitchen, to maintain overall conditions.  You might want a small fan to assist with kitchen odours though.

 

We do have an extract fan in our kitchen, as an easy route for passive stack was not available. 

 

Building from scratch, these problems could all be mitgated at the design stage. 

[SimonD]

On 20/02/2026 at 15:57, Nickfromwales said:

So no mechanical fans in kitchen / utility / bathrooms etc?

 

If it's all properly designed, there's no need for them, but BCO might ask for them to be installed. I have an old inline fan in a cupboard in the kitchen but not connected, another in the guest bathroom not connected and a small one in the ensuite that I've just put in at minimum fan speed because my wife was worried.....

[sgt_woulds]

One of the drawbacks I can see with iPSV is hot days and sustained heatwaves with little wind to drive ventilation.

 

Currently we 'sail' or house through heatwaves by closing off all ventilation and shading the south facing windows (curtains, but we are planning external shades when we replace the front windows). 

 

Our roof and walls contain lots of woodfibre so we have good decrement delay, and occupation is low during the day so CO2 and moisture levels are not an issue.  In the evening after the sun has set and the air temperature has dropped, we open the north facing windows and the skylight and purge ventilate the house - you can feel the cooler airflow and it is very refreshing.

 

However, after a couple of days of heat, the night time temperature difference is reduced (due to radient heat from the earth and buildings) so this option tails off and CO2 levels inevitably rise.  We then use portable fans to make life bearable.

 

I know they considered this issue with the Bedzed buildings and tried using ventilation cowls / wind catchers but I don't think it was very successful. 

 

It is pretty much a given that climate change will lead to more frequent and longer heatwaves so I'm considering building a solar chimney with soil pipe ventilation - I have to build a patio out the back anyway so it is just a little extra excavation.

 

The chimney might be an issue with building control, but sod 'em!  We'll stick it up and see if anone notices!  I have a couple of ideas on the design, and I'm considering buying the Handbook of Domestic Ventilation but I don't know if this is a good sourceof information or if there is better text elsewhere.  It is an expensive book to take a punt on...

Edited yesterday at 09:56 by sgt_woulds
missing words

[Bancroft]

4 hours ago, sgt_woulds said:

have to build a patio out the back anyway so it is just a little extra excavation.

If your patio/back garden is big enough, how about an earth tunnel?

 

I was quite keen on trying to incorporate one into our new build but the architect just went into tilt mode whenever I tried to bring the subject up.  Just wasn't on his radar so didn't exist in his mind.

[JohnMo]

1 hour ago, Bancroft said:

how about an earth tunnel?

Aren't these a bit - yes they work great at bring in stable air temperatures, but can also bring all sorts of pathogens and bad stuff over time, so not the be all, end all solution? Plus you definitely need forced mechanical ventilation.

 

 

[Gone West]

1 hour ago, Bancroft said:

how about an earth tunnel?

That is something I looked at when designing my new build. I looked at the Rehau system which used silver plated ducting to kill off any bugs, but it was too expensive. That was sixteen years ago though, so things might have improved.

[saveasteading]

36 minutes ago, JohnMo said:

Aren't these a bit......

I've no idea because I have only heard of them in "wind in the willows".

I hope it's actually a plastic pipe with a riser and rain/mouse barrier.

If it's meant to prewarm the air then that won't work past November.

[SteamyTea]

I just happen to be looking at some ground temperature data.

I am not so sure it is a good idea to bury air pipes in the ground, even at 1m depth, it is only from mid March to September that the ground is cooler than the air, and then only by a maximum of 2°C.

At the half metre it is about 1.5°C cooler.

I also suspect that the energy transfer efficiency is not too good.

 

[Iceverge]

I looked at earth tunnels when we built but came to the same conclusion as @Gone West. 

 

Minimal energy gain with the drawbacks of mould growth in the pipe and high install costs. 

 

As usual sitting down with a calculator and a biro very quickly dispells incompletely though out ideas. Passive stack was another. 

 

There's only 3 practical options really.

 

1.Trickle vents and extractor fans if you don't care about indoor air quality, noise, thermal comfort or energy use. 

 

2. Humidity sensitive mechanical extract. Upgrade to humidity sensitive vents if possible. Good IAQ. Some energy loss.  Minimal maintenance costs but some cold  spots in the house. 

 

3. MVHR. Excellent IAQ, minimal energy loss, best thermal comfort, no cold spots or noise. Higher maintenance costs may not be offset by lower ventilation losses. 

 

 

 

 

 

 

 

 

 

[sgt_woulds]

16 hours ago, SteamyTea said:

I just happen to be looking at some ground temperature data.

I am not so sure it is a good idea to bury air pipes in the ground, even at 1m depth, it is only from mid March to September that the ground is cooler than the air, and then only by a maximum of 2°C.

At the half metre it is about 1.5°C cooler.

I also suspect that the energy transfer efficiency is not too good.

 

 

These only list temperatures at 1m depth, which is barely below the subsoil in most regions.  We are on solid chalk and our topsoil depth is only about 300mm max.   At depths of 1.5 to 2m the rock should be at stable temperature.

 

In Hungary i've visited peasant wine cellars built into slopes where the depth above the vaulting is less than two metres and the resulting drop in air temperature is very noticable even in sustained heatwaves.

 

19 hours ago, Bancroft said:

If your patio/back garden is big enough, how about an earth tunnel?

 

 

Soil pipe / Earth tunnel.  Same thing - just don't confuse it with the other type of soil pipe 🙂

 

 

 

17 hours ago, saveasteading said:

I've no idea because I have only heard of them in "wind in the willows".

I hope it's actually a plastic pipe with a riser and rain/mouse barrier.

If it's meant to prewarm the air then that won't work past November.

 

Cooling only. 

 

I gather it is quite popular in French public buildings and schools & used by enviro-mentalists (like me 🙂 ) in California .

 

Measures need to be taken to ensure that rain/rodents etc cannot get in.  I suspect that clay pipes would work better than plastic to for energy transfer.

 

13 hours ago, Iceverge said:

I looked at earth tunnels when we built but came to the same conclusion as @Gone West. 

 

Minimal energy gain with the drawbacks of mould growth in the pipe and high install costs. 

 

 

 

It's not about energy gain, this is about drawing in cooled air for sustained high temperature situations where subsoil and rock maintain a lower temperature.  Even a 2 degree drop from ambient air temperature can be a significant health benefit in a sustained heatwave.

 

 

13 hours ago, Iceverge said:

As usual sitting down with a calculator and a biro very quickly dispells incompletely though out ideas. Passive stack was another. 

 

There's only 3 practical options really.

 

 

 

Could we see your sums on this?

 

Are you talking about a planned and 'intelligent' passive stack in a well sealed or even 'passive' house or retrofit to leaky fabric?

 

If it is the latter, then none of the ventilation options are perfect...

 

 

 

 

[sgt_woulds]

 

Talking of sums, this is a bit out of date now (I saved this about 5 years ago), but posted for further discussion:

 

 

 

 

This does not include running costs.  Perhaps someone here can update the MVHR / MEV costs based on real life experience. 

 

I've costed iPSV componants at around £800 for my small 3 bed, two storey house. at current prices

 

 

Edited 38 minutes ago by sgt_woulds
missed text

[SteamyTea]

12 minutes ago, sgt_woulds said:

These only list temperatures at 1m depth, which is barely below the subsoil in most regions

Well at 0.1, 0.2, 0.3 and 0.5m depths, which is about the normal depths for foundations.

 

There are many things that will affect the temperature at different depths, hours of sunlight and rainfall are probably the biggest factors. I think that data is available from the RU website. Wish I had more time to look at it all.