Off-grid new-build timber A-frame in Caithness, NE Scotland

[Ed Davies]

Hello all. And hello again to the many names I recognise from other forums.

 

I'm currently in the process of building a new timber-frame (post and beam, sort of Segal method) A-frame house on a rather exposed hill top in NE Scotland, overlooking the Moray Firth. I have a blog (https://edavies.me.uk/blog/) with entries specifically about the house tagged Perihelion (the house's name).

 

Apart from an Internet connection the house will be completely off grid. The notion is that it's a “no-combustion” house - no energy comes from burning stuff like oil, gas, coal, peat, wood or whatever, just (through a couple of levels of indirection) from fusion roughly one astronomical unit away either via solar thermal (hot water evacuated tube panels) and PV on the roof and, perhaps, from a small wind turbine though that's something I'd rather avoid. We'll see.

 

Part of the idea is a large thermal store - roughly 10 tonnes of water in tanks within the thermal envelope to allow energy collected during late summer and autumn to supplement the small amounts collected in the short days of the core part of the winter.

 

The water supply will be rainwater harvested from the roof. Drought is rarely a problem here though the dry ground a few weeks ago did give cause for thought: in particular it occurred to me that using water from the thermal store for toilet flushing during summer might stretch the store significantly.

 

There's more about the design in the planning application Design Statement: 3rd from bottom PDF here: https://wam.highland.gov.uk/wam/applicationDetails.do?activeTab=documents&keyVal=N09ALOIH7R000

 

The whole build has been frustratingly slow mainly because of the weather. Rain has given plenty of rest days, of course, but the main problem has been wind. E.g., today looks like the last calm day for a while to allow me to put the last of the membrane up on the west gable but it's looking like it'll be raining pretty steadily all day. And so it goes.

[Guest Alphonsox]

Welcome to the forum - This sounds like a really interesting project, looking forward to hearing more about the details.

[Nickfromwales]

Hi and welcome to our new hideout . 

Im intrigued as to where this 10 tonnes of water will sit? 

Ill definitely be looking at the links later, some evening reading. 

Always pricks my ears up when I hear "off - grid". 

[ProDave]

Hi and welcome. That#s now 2 members further north than me.

 

I would say with your location, a wind turbine is a no brainer.

[Stones]

Hi Ed, and welcome. I'm a little further north (and a ferry ride) away from you, but can certainly relate to the weather!

 

Hopefully I'll be able to stop by your build at some point when I'm heading south.

[Ed Davies]

1 hour ago, Nickfromwales said:

Im intrigued as to where this 10 tonnes of water will sit? 

 

It's an east-west A-frame built over a post-and-beam frame. Here's a view looking towards the west gable at the end of last month when I hadn't yet put the last two triangular bits of OSB in the top. The thermal store will go along the north side (to the right of the posts). That's part of why I went for an A-frame, normally the “wings” there are considered a waste of space but I have a use for them.

 

Window holes to be cut in the south roof later.

[Ed Davies]

1 hour ago, Stones said:

Hopefully I'll be able to stop by your build at some point when I'm heading south.

 

Absolutely, I'm always pleased to talk to people on site. There's a contact details page on my website.

 

I do like Orkney and seriously considered a plot north of Finstown (went as far as making an informal offer). Combination of the seller wanting a bit more money (“offers over”) and restrictions on the building season due to breeding on the adjoining bird reserve put me off pursuing it further. Plus the probable extra cost of material shipped there. But I did find it a very friendly and pleasant place and admire the amount of renewable energy and joined-up projects there.

[Stones]

Out of interest, where was the plot you looked at? From what you describe somewhere near Cottasgarth?

[Ed Davies]

 

Yes, close to there. Other side of the A996 and a little way south. I think this is the entrance track to it:

 

Street Map

 

[Nickfromwales]

14 hours ago, Ed Davies said:

That's part of why I went for an A-frame, normally the “wings” there are considered a waste of space but I have a use for them.

Agree its a wasted space otherwise, but what will keep 10 tonne there? Will the weight simply be spread over a long distance and things beefed up as required? Bespoke tanks ?

Its an interesting idea so im keen to better understand it. Thanks. 

[Triassic]

Welcome, I’m sure I’ve read your posts elsewhere? 

[Onoff]

Hello and welcome. I dip in occasionally to an American solar forum. It's a bit clunky to navigate I find but they're a friendly bunch. A lot make their own heat storage tanks. Size I suspect often makes up for inefficiency but then they have the space. Worth a look:

 

http://simplysolar.supporttopics.com/?forum=268124

[Ed Davies]

11 hours ago, Triassic said:

Welcome, I’m sure I’ve read your posts elsewhere? 

 

Indeed - your pseudonym is one I recognize from GBF (and also, longer ago, Navitron, perhaps, where I used the handle EccentricAnomaly) so hello again. Ditto Stones, SteamyTea, JSHarris, etc.

 

[Ed Davies]

12 hours ago, Nickfromwales said:

Agree its a wasted space otherwise, but what will keep 10 tonne there? Will the weight simply be spread over a long distance and things beefed up as required? Bespoke tanks ?

Its an interesting idea so im keen to better understand it. Thanks. 

 

Site-made tanks. Timber frame with EPDM liners. Quite commonly done by people in the US. Not very deep as the there's a reasonable length to play with (about 13 metres) so the weight will be pretty spread out. It was, of course, taken into account in the structural engineering.

[Jeremy Harris]

11 minutes ago, Ed Davies said:

 

Site-made tanks. Timber frame with EPDM liners. Quite commonly done by people in the US. Not very deep as the there's a reasonable length to play with (about 13 metres) so the weight will be pretty spread out. It was, of course, taken into account in the structural engineering.

 

 

Sounds like a very neat solution to making insulated tanks.  I'll be very interested in the performance, as a couple of years or so ago I read of a similar store that was built using a cylindrical tank that ran up the centre of the building, with the stair case wrapped around it.  Sadly I can't remember where I read about it; may have been in the Passive House magazine.

 

On a vaguely related topic, many years ago a friend (who, it has to be said, is slightly more eccentric than I am...) converted an old chapel into a house.  He built a hollow insulated blockwork square section "tower" in the centre of the chapel and filled it with large granite rocks that he collected from the beach, one by one in the back of his 2CV.  In between the rocks he laid resistive heating elements stripped from old storage heaters (together with the iron blocks), modified to run from a low voltage supply.  He used a home made wind turbine to "charge" this big thermal store, and had ducts with low voltage fans and shutters that led from the store to each heated room.  The system worked very well, although he was in a good position for getting a reasonable amount of wind power, on top of a hill in South West Cornwall.  By a very weird coincidence my great grandfather had been the minister at that chapel around 1900, and my great aunt was born in the house alongside.

[Square Feet]

I have long been interested in the Segal method and also passive house and off-grid houses so it was very interesting to read some of your blog and see your progress.  

I shall be particularly interested to see how you go about insulating the floor as that seems to be the biggest issue with a Segal type foundation system.   I came to the conclusion that Segal and passive were mutually-exclusive, but I would be happy to be proved wrong on that!

[Ed Davies]

Square Feet: yes, it's not easy as Segal really means a bit of a gap underneath which then has to be high enough to allow attaching whatever underfloor sheet you use to under the joists resulting in the house being yet taller.

 

In my case I have nominal 400mm under the floor (bit more at the west end, bit less at the east), sarking boards, 220x45 joists which will be infilled with mineral wool then they'll be 145x45 joists running perpendicular also infilled with mineral wool, 22mm T&G chipboard then finish floor (probably cork tiles in bedrooms and shower room,  laminate in hall, kitchen, living room and study). Result is that finish floor winds up nearly 800mm above ground level which is not insignificant. As it works out the ground level in the house area is some 400mm below the parking area so in this case an accessible ramp up to the level of the house is not a big deal but if things were the other way round that'd be quite a structure.

 

An alternative which was suggested on another forum would be to have the joists closer to the ground, board round the sides, then fill the whole void with EPS beads. I'm not sure if you'd need a DPM or whether you could sensibly rely on the EPS not wicking. If I'd tried that with my joists at the height they are it'd needed about 600mm depth so 60m³ of beads which seems a lot but would have been cosy. Maybe next time ;-).

[Ed Davies]

2 hours ago, JSHarris said:

He built a hollow insulated blockwork square section "tower" in the centre of the chapel and filled it with large granite rocks

 

I like the idea of that. Of course granite tends to have of the order of half the volumetric heat capacity of water. Not sure about blowing air through though as I'm not sure you'd want to breathe what comes out. That's an advantage of water as a store - it's relatively easy to circulate to extract heat if simple percolation out turns out not to be sufficient. The disadvantage of water is that it's a bit more spilly than granite.

[Jeremy Harris]

Back when he built his granite thermal store I think the Radon risk was not yet widely known or understood.  I do remember back in the early 70's borrowing a Geiger–Müller counter from work and taking it back home to Cornwall one weekend and seeing how active some of the granite outcrops on Porkellis Moor (behind where my mother then lived) were and being surprised to find readings that were well in excess of 10,000 cps, far higher than we would have accepted for any contamination in the lab at work.

[Nickfromwales]

@Ed Davies

Ed, if you wish to 'mention' another member simply type the @ symbol and then the first couple of letters of their ID and then select from the drop down list that will appear.  Like I have done above. 

To quote a segment of others posts just select the section of text and 'quote selection' will appear. Click that and it'll open the editor with that person notified that you have quoted them. 

Anything else you need to know just ask  

[Square Feet]

3 hours ago, Ed Davies said:

Square Feet: yes, it's not easy as Segal really means a bit of a gap underneath which then has to be high enough to allow attaching whatever underfloor sheet you use to under the joists resulting in the house being yet taller.

 

In my case I have nominal 400mm under the floor (bit more at the west end, bit less at the east), sarking boards, 220x45 joists which will be infilled with mineral wool then they'll be 145x45 joists running perpendicular also infilled with mineral wool, 22mm T&G chipboard then finish floor (probably cork tiles in bedrooms and shower room,  laminate in hall, kitchen, living room and study). Result is that finish floor winds up nearly 800mm above ground level which is not insignificant. As it works out the ground level in the house area is some 400mm below the parking area so in this case an accessible ramp up to the level of the house is not a big deal but if things were the other way round that'd be quite a structure.

 

An alternative which was suggested on another forum would be to have the joists closer to the ground, board round the sides, then fill the whole void with EPS beads. I'm not sure if you'd need a DPM or whether you could sensibly rely on the EPS not wicking. If I'd tried that with my joists at the height they are it'd needed about 600mm depth so 60m³ of beads which seems a lot but would have been cosy. Maybe next time ;-).

 

Rather you fit the membrane and tapes underneath than me....  Best of luck with it all - it's a really interesting concept.

[Ed Davies]

3 hours ago, Square Feet said:

Rather you fit the membrane and tapes underneath than me....

Membrane and tapes will go on top of the sarking. I think (and hope) I won't have to work under the house again [¹]. There'll be weatherboarding round the edges anyway and the space below will be ventilated so there's no more need to protect the sarking than, say, normal floorboards over a crawl space.

 

Actually, I'm thinking of using 20mm EPS rather than membrane on top of the sarking, between the joists. Reason being is that it gives a tiny bit more insulation and costs about the same as using a membrane given that it saves 20mm of mineral wool and leaves me with a round 200mm gap to fill which can be done more easily with the mineral wool I have in mind.

 

[¹] Edit to add: Other thread reminds me, will have to go under again for soil pipe.

Edited August 15, 2018 by Ed Davies