Hello from sunny Surrey

[Caroline]

Hello all

 

We bought a several acres of green belt land (ancient replanted Woodland) in 2017.  We have full planning permission for 2 detached houses 174sqm each and one barn style detached house 137sqm.

 

We plan to build one for our own residential property and sell two plots, one plot 0.6 acres the other 0.13 acres.

 

We haven been approached by several developer but would rather sell to other “self builders”.

 

We are planning to build an Oak Framed house using SIPS in a traditional cottage style.

 

Has taken a lot of effort to get to the point we are at now, have self build Mortgage in Principle.

 

One thing I am struggling with is getting Geothermal Piling quote. We need piled foundations so thought if we could get the bore holes deep and use for ground source heat (although we have a woodland management plan about to be approved, not the best area for loop heat source). I’ve emailed three piling companies who say they do geothermal piling but they have emailed back to say they don’t!

 

Apologies if any of you have dozed off reading my introduction but you can imagine, I have loads of questions, which will follow in due course?

 

Best wishes

[MikeSharp01]

Welcome to THE self build forum. Sounds like an interesting project all round.  You purchased green belt and got planning permission - how? 

 

There must be piling companies who do this just a case of finding one - someone will be along shortly who has some insights. 

[PeterW]

Welcome ..!

 

Just a thought - given the cost and complexity of using geothermal can you not design this out and use ASHP or similar and also improve thermal insulation levels to reduce heat loads..? 

 

Geothermal piling is a niche market and you are going to pay a lot for something that can be solved in better ways. 

[Declan52]

How do you know for definite you need piles??

Could an insulated raft not be an option instead??

 

[Caroline]

Wow, quick responses, thank you.

 

We purchased with planning permission but increased volume and we think, designed a better build.

 

We had soil samples taken and in view of the quantity of trees and soil, piling to two of the three properties was recommended.

 

Have considered ASHP, but received mixed reviews from users.  Any recommendations on area without mains gas are welcome.

 

Will be installing thermal raft.

 

Thanks all  

[ToughButterCup]

13 minutes ago, Caroline said:

[...]

We had soil samples taken and in view of the quantity of trees and soil, piling to two of the three properties was recommended.

[...]

 

Here be dragons. Have a look at this

[Caroline]

Hi Recovering Academic

 

I've read your link amd unfortunately not being an academic myself can't make head nor tail. Do you think Surefoot could help us? I have soil sample report and obviously would like to save money wherever possible. I wasn't impressed with our SE (won't go into that) but really need another, however, lots approached are not familiar with Oak Frame and Oak Frame manufacturer say they so the calculations and SE isn't needed. We do have an architect but Oak Frame manufacturer has done the drawings (not detailed ones for building control, these are yet to be completed)

 

Thank you

[Jeremy Harris]

Unless you're on clay that's prone to a lot of heave, shrinkage and movement, then I'd have thought a passive slab would be cheaper, quicker and a lower risk than piling.  A passive slab can be made to work with poor ground conditions by just increasing the depth of the crushed stone sub-base, and generally imposes a low over bearing load on the underlying soil, making it idea for most poor ground conditions.

 

It's a concept that is still relatively uncommon, as it's only been around for ten years or so, and the building industry seems to be very reluctant to accept anything "new", but our house is built on gault clay with a passive slab an the foundations took 4 days to put in, start to finish (including fitting all the ground floor UFH pipes).

[Caroline]

8 minutes ago, JSHarris said:

Unless you're on clay that's prone to a lot of heave, shrinkage and movement, then I'd have thought a passive slab would be cheaper, quicker and a lower risk than piling.  A passive slab can be made to work with poor ground conditions by just increasing the depth of the crushed stone sub-base, and generally imposes a low over bearing load on the underlying soil, making it idea for most poor ground conditions.

 

It's a concept that is still relatively uncommon, as it's only been around for ten years or so, and the building industry seems to be very reluctant to accept anything "new", but our house is built on gault clay with a passive slab an the foundations took 4 days to put in, start to finish (including fitting all the ground floor UFH pipes).

Unfortunately is clay and worried that if we don't have trad piles there could be issues with heave

[Jeremy Harris]

Worth talking to one of the SEs that are familiar with passive slab design, though, as you may find that you can just increase the depth of stone under the insulation to both reduce the bearing load and get below the heave zone.  It's usually a fair bit cheaper and quicker to just add more stone than it is to bring in a piling rig.  We costed up using piles and they were going to be both more expensive and take longer to put in than just digging out the base area a bit deeper and adding stone.

[PeterW]

11 minutes ago, Caroline said:

Unfortunately is clay and worried that if we don't have trad piles there could be issues with heave

 

Have you got the soil survey ..? Piling is not the only option on clay and near trees, and sometimes it can be a worse option as you need to bring in large equipment that needs more earthworks than a passive slab. 

[pdf27]

With regard to ASHP/GSHP, how highly insulated are you planning to go? A Passivhaus is 10W/m² at the design low temperature condition, so at that heat load the biggest house would need 1.7kW of heat on a cold day in Winter (50 kWh/day). Assuming a GSHP has a COP of 4 and an ASHP a COP of 3, that's 12.5 kWh of electricity for the GSHP and 16.5 kWh for the ASHP, for a cost difference of about 50p on an unusually cold day. ASHPs are actually better than GSHPs for producing hot water in summer, so over the course of a year then for a low energy house then the running cost difference is pretty trivial while the installation cost difference is potentially very large in favour of the ASHP.

 

Things are different if you're just designing to meet the minimum building regs requirement - there your heat loads are far higher and a GSHP starts to make a lot more sense. For me personally that's the wrong way to go though - I suspect in 90% of cases the cheapest way to a particular fuel bill is an ASHP plus more insulation rather than a GSHP. There will be exceptions of course (acres of north-facing glass with a lot of shading, hard to insulate retrofits, etc.) but I suspect it's probably a pretty good general rule.

[Caroline]

17 minutes ago, PeterW said:

 

Have you got the soil survey ..? Piling is not the only option on clay and near trees, and sometimes it can be a worse option as you need to bring in large equipment that needs more earthworks than a passive slab. 

Yes have the extensive long soil survey, do you fancy some bed time reading ?

[Caroline]

6 minutes ago, pdf27 said:

With regard to ASHP/GSHP, how highly insulated are you planning to go? A Passivhaus is 10W/m² at the design low temperature condition, so at that heat load the biggest house would need 1.7kW of heat on a cold day in Winter (50 kWh/day). Assuming a GSHP has a COP of 4 and an ASHP a COP of 3, that's 12.5 kWh of electricity for the GSHP and 16.5 kWh for the ASHP, for a cost difference of about 50p on an unusually cold day. ASHPs are actually better than GSHPs for producing hot water in summer, so over the course of a year then for a low energy house then the running cost difference is pretty trivial while the installation cost difference is potentially very large in favour of the ASHP.

 

Things are different if you're just designing to meet the minimum building regs requirement - there your heat loads are far higher and a GSHP starts to make a lot more sense. For me personally that's the wrong way to go though - I suspect in 90% of cases the cheapest way to a particular fuel bill is an ASHP plus more insulation rather than a GSHP. There will be exceptions of course (acres of north-facing glass with a lot of shading, hard to insulate retrofits, etc.) but I suspect it's probably a pretty good general rule.

Thanks so much. Do you have ASHP? If so, what system/manufacturer? Have you had it long amd are you happy with it?

[Caroline]

24 minutes ago, JSHarris said:

Worth talking to one of the SEs that are familiar with passive slab design, though, as you may find that you can just increase the depth of stone under the insulation to both reduce the bearing load and get below the heave zone.  It's usually a fair bit cheaper and quicker to just add more stone than it is to bring in a piling rig.  We costed up using piles and they were going to be both more expensive and take longer to put in than just digging out the base area a bit deeper and adding stone.

Thank you, will bear in mind

 

 

[PeterW]

ASHP can be installed DIY too - it’s two cables and two pipes. 

 

GSHP is a whole different ball game ..! 

[Onoff]

How about building a lake and having a water source heat pump?

[pdf27]

18 minutes ago, Caroline said:

Thanks so much. Do you have ASHP? If so, what system/manufacturer? Have you had it long amd are you happy with it?

Not yet - I'm hoping to demolish & rebuild our existing house, just getting the money sorted at the moment (we bought it planning to refurbish but by the time we did everything it's cheaper to start again). One thing I've been looking at quite a lot is heat pumps - my wife is from the US and every year for the week or so when the weather is hot and humid I have to listen to her bitching and moaning incessantly about the fact that "this goddamn country doesn't have air conditioning". This means that - despite the fact that we have mains gas available on site - we're going to be doing a heat pump because it can also provide cooling. I'm also a chartered engineer working in R&D so doing things like setting up a spreadsheet to work out actual COP based in predicted heating/hot water loads and historical air temperatures comes pretty naturally.

Instinctively I'd prefer to have a GSHP, but I just can't get the numbers to work out even though I've got a garden big enough for it. Based on 2016 data and published COP curves for a Samsung heat pump I'm predicting something like a COP of 4.4 for heat at 25C and 2.8 for hot water at 55C over the course of a year - and total electrical consumption of 1000-1500 kWh over the course of a year. By the time you get to that point there really isn't very much scope at all to reduce electrical consumption by going from an ASHP to GSHP - and the amount of extra money you need for a GSHP install is enough to make a big reduction in heat demand. You end up with the situation where a GSHP install costs maybe £10k extra including ground works, etc. in return for a modest reduction in sound levels. The logical conclusion to this is that alternative ways to reduce noise from an ASHP should be considered, and that given the cost differential it should be possible to throw a shedload of cash at this problem and still come out ahead.

Looking at the noise ratings for split heat pumps is instructive here - the indoors units are very quiet indeed, quieter than an equivalent GSHP in fact, and the noise comes from the outdoor units. This appears to be predominantly flow noise from the air - and silencing air flow noise is something that is done all the time with commercial air conditioning systems. Segregating air flow should also be pretty straightforward, since the blows air out of the fan hole at the front and is sucked in everywhere else. So I'm thinking of maybe putting the outside unit in the loft of an attached garage, with louvres along the lines of http://www.wakefieldacoustics.co.uk/products/acoustic-louvres/ at either end wall, and the ASHP unit outlet directly ducted onto one of the louvres with some draft excluder, using the garage loft as essentially a giant air duct. Not a perfect solution, but looking at the sound curves at maximum power it would be about 35 dBa, mostly in the low frequencies which I can tolerate slightly better. Given that this will be outside the house and the house itself will further attenuate any noise (and ideally it would be at the front of the house so further shielded from the back garden), that should be good enough.

 

So far as brands and reliability goes, any of the big brands should be fine - the main thing to be wary of is that the MCS installers tack a lot onto the price for the privilege of claiming the RHI payments, so it probably isn't worth going down that route. Monobloc units are probably easier to fit (there are a number of people on the forum fitting them as a DIY or quasi-DIY job), while split units need someone with an F-gas license to fit. That isn't too hard though - you'll have any number of small air conditioning companies local to you who could fit it, so it shouldn't cost too much. I'm personally leaning that direction, mostly because I think it should make the plumbing design a lot simpler.

[Jeremy Harris]

My experience has been that the published COP curves are unrealistic, as the killer is humidity, rather than temperature, and it's hard to get hard data for the combination of the two and the way the defrost systems impact on COP.  I spent a lot of time fine tuning the settings on our ASHP, and in the end managed to get it working so it very rarely, if ever, defrosts.  This has a massive impact on COP, as the defrost cycle runs the heat pump in reverse for around 10 minutes, pumping heat out of the house, so just one defrost cycle per hour knocks 30% off the true COP.

 

Our ASHP has temperature and RH sensing at the air intake, and uses some form of combination of the two, together with the heat pump operating power, to try and predict when a defrost cycle is needed.  I found by experiment that adjusting the weather compensation to remove it, and setting the heating output temp to 40 deg C, resulted in virtually no defrosting for our installation.  Our ASHP is significantly over-sized for the heating requirement though; it's a nominal 7 kW rated output unit that rarely needs to deliver more than 1 kW to the floor heating.

 

I worked out that it just wasn't worth paying the big premium for an MCS install, as for us the RHI would only have been around £80 or so per year for 7 years, and the MCS premium was well over £2,000.  I knew nothing about installing these things and had it installed in a day, just two pipes and two cables, it really couldn't have been simpler.  I did spend a lot of time tuning it to improve the COP though, and it now runs at over 3.5 on average and exceeds 4 from time to time.

[SteamyTea]

Welcome.

Re your groundwork/foundation/piling, it may be worth having a word with @joe90.  He built on the flattest bit of land in the West Country, and it was very boggy.  His local Building Control was happy with trenches.  I know little about foundations, and each house seems to have unique issues, though I think half of that is lack of knowledge about alternatives by builders/SEs/BCs.

 

As for SIP's  Have you checked the U-Values and associated thicknesses of the panels.  You may need secondary internal/external insulation fitted.

 

I have stood next to both @JSHarris's ASHP while it was running, and next to @joe90's with it was not.  There was no difference in noise.

 

@JSHarris you may have missed my post about monitoring an ASHP for frosting, I am looking to put some kit on a couple or three.

 

[Jeremy Harris]

3 minutes ago, SteamyTea said:

@JSHarris you may have missed my post about monitoring an ASHP for frosting, I am looking to put some kit on a couple or three.

 

 

I could relatively fairly easily add an external RH sensor, I think.  I already log ASHP flow temperature, floor temperature and outside air temperature just above the intake to the ASHP on the North face of the house.  Currently the logger records a set of readings every 6 minutes, and stores the data in 1 month chunks, using a GPS master clock to keep the timing consistent.

[joe90]

As per Steamy,s post above, yes our site is very flat, thick yellow clay and very boggy. The local building control guy was happy with trench foundations and asked for 800mm deep and 700mm wide ( our walls are brick and block outer and inner with 200mm full fill cavity with Rockwool ) we installed a French drain around these (back-filled the trench outside with 50mm stone) and piped it to a local ditch. The foundation detail was as follows to avoid cold bridges and I am very happy with it, we did not need an SE to design or sign it off..You mentioned “cottage”, ours too is cottage

 

P.s. we also have a DIY installed ASHP ( which I have yet to fire up).

[jack]

11 hours ago, joe90 said:

 

This would have been better as a 1.5 storey cottage. Much more in keeping with the local vernacular.

[Caroline]

43 minutes ago, jack said:

 

This would have been better as a 1.5 storey cottage. Much more in keeping with the local vernacular.

Hi Jack

 

Our house is 1 1/2 storey, and I’ve seen one built and it’s fine, however, you would be surprised at the couple of interested people in one of the plots for sale want two storey. 

 

Bigger seems to to be better for most, not sure why?

[jack]

1 minute ago, Caroline said:

Our house is 1 1/2 storey, and I’ve seen one built and it’s fine, however, you would be surprised at the couple of interested people in one of the plots for sale want two storey. 

 

Bigger seems to to be better for most, not sure why?

 

Ah, sorry, it's a joke based on the long planning history of this house. Joe's local council were insisting on 1.5 storey based on a mythical "local vernacular" requirement. He took it to appeal and won.