Generally - Wall/Slab/Roof build-up advice for very large new build.

[ElliotP]

Hi All,

 

So we're finally pushing ahead with our new build and I'd really appreciate some advice about the construction options available.   We're a the planning stage, and have appointed an architect.   I'll be project managing the build and doing the majority of internal work myself, but I'll be contracting the foundation, slab, walls, roof.  The build will be quite large; a 6 bedroom house, over 3 floors, sizeable living rooms, kitchen.  A swimming pool and gym. A connected triple garage and a 3 bedroom annex as well.   Budget wise I'm not looking to go all-out, it will be *relatively* tight, so given the size of the build an economical (yet thermally efficient) build-up will result in significant construction cost savings.  While I want to get close to passive haus standards, cost-benefit will be more important to me, such as not spending £50k in construction costs to gain thermal savings of £500 a year on heating for example (pie in the sky figures but you know what I mean).  

Heating will be ASHP or GSHP depending on costs and benefit again.  Plenty of solar and battery storage.  The style of the house is going to be something like the below but on a larger scale, with the majority of glass being north facing, solar gain shouldn't be too serious.

 

From my point of view, I think the primary choice should have been timber frame, however I don't think it's going to make sense in terms of budget when we need facing bricks anyway.  Therefor I was thinking more towards a traditional buildup, facing bricks, semi-wide cavity, blockwork on the inside.  As I have seen mentioned in this thread by @PeterW , something like:

100mm brick

175mm cavity (widest before ties get expensive) blown EPS

100mm medium block

Bonding parge coat

25mm batten Infil with 25mm PIR

Board

Skim

As mentioned in that thread, with that build up you can use standard lintels which keeps cost down.  Anything after the medium block I can handle myself too.

For roof; which will be timber framed, and a passive roof system along the lines of one of the options here: https://www.firstinarchitecture.co.uk/passivhaus-roof-details/

For the foundation and slab.  Some kind of Passive slab system such as http://www.viking-house.ie/passive-house-foundations.html ?

Would appreciate any input on any of the above.  What have you done? What should be avoided? 

Thanks in advance.

 

[Dave Jones]

no offence but its not going to be lintels that break this one. Whats your QS m2 price  ?

 

Pick anything out the ordinary like passiv roofs and you are adding ££££ as you are limiting the trades available with experience.

 

Unless your plan is to be complete in 12-20 weeks shed build is a waste of money. 

 

Simplify everything you possibly can.

[nod]

I would have perhaps started with your location and budget 

I found that using 70 mil insulated plasterboard dabbed directly onto the exterior walls has worked a treat on our previous build Hopefully does the same on our current build 

With three vaulted ceiling’s I’ve used 120 insulation between the rafters and taped them in multi foil 

[SteamyTea]

15 hours ago, ElliotP said:

For the foundation and slab.  Some kind of Passive slab system such as http://www.viking-house.ie/passive-house-foundations.html ?

Do not deal with Seamus, he can causes loads of trouble.

 

I think that foundation system is a Kore one, which is pretty good.

 

[jack]

Interesting looking build, hopefully you can share more details in due course.

 

18 hours ago, ElliotP said:

Heating will be ASHP or GSHP depending on costs and benefit again. 

 

I think we've probably reached the point where GSHP is simply not a cost-effective option compared to ASHP. There might be the odd special case where you have a large field next door that you were going to massively dig up anyway, in which case GSHP might approach price competitiveness.

 

But in general, GSHP setups are at least double to price of an ASHP of the same output. If properly done (and that isn't always the case), the GSHP will have slightly higher efficiency, but not enough to ever pay back the price difference.

 

 

 

 

[SteamyTea]

2 minutes ago, jack said:

There might be the odd special case where you have a large field next door that you were going to massively dig up anyway

Or you have noise or view restrictions and little space i.e. town centre.

 

A GSHP would fit my place nicely as I am in  World Heritage Site.

[jack]

6 minutes ago, SteamyTea said:

Or you have noise or view restrictions and little space i.e. town centre.

 

That's true.

 

Still, in a town centre, you'd probably need to use vertical boreholes, which add significantly to the cost.

[SteamyTea]

7 minutes ago, jack said:

Still, in a town centre, you'd probably need to use vertical boreholes, which add significantly to the cost.

Yes,

But down here, if you can get drinking water out of it, you can save there (we have the most expensive water and sewage in the country).

Edited March 19 by SteamyTea

[saveasteading]

24 minutes ago, jack said:

odd special case where you have a large field next door that you were going to massively dig up anyway, in which case GSHP might approach price competitiveness.

That's the slinky or ground loop? It relies on summer reheating of the ground surface. It is also now agreed that it may need additional seasonal heat from reversing the sysyem and / or adding solar.

[jack]

18 minutes ago, SteamyTea said:

Yes,

But down here, if you can get drinking water out of it, you can save there (we have the most expensive water and sewage in the country).

What's the payback time on a £30k+ borehole system for you?

[jack]

12 minutes ago, saveasteading said:

That's the slinky or ground loop? It relies on summer reheating of the ground surface. It is also now agreed that it may need additional seasonal heat from reversing the sysyem and / or adding solar.

 

Yes, that's the one. I've heard horror stories about badly implemented slinky systems. I'm sure there was someone on BuildHub a couple/few years ago who had problems with the ground over their system freezing towards the end of winter.

 

My main point is that there are only very limited situations in which a GSHP will make sense over an ASHP.

[SteamyTea]

31 minutes ago, jack said:

What's the payback time on a £30k+ borehole system for you?

A long time.

 

Back of a fag packet calculation (will need a white marker now as the packets are black).

 

Current space and DHW ~2865 kWh/year, at current rate of 16p/kWh, £460.  If that became 1/4^rd of the price (CoP = 4) then £115 energy cost

Water is 0.17m³/day, so 62m³/year, water is £1.9338/m³, so £120/year.

So

30,000 [£] / 235 [£] = 128 years (house is currently 37 years old)

Those are without VAT.

If I was a bit sneaky and did not pay for the sewage, then I would save another £200. Sewage is £3.2871/m³ for 95% of usage, Standing Charge is £150.86/year

So 69 years.

 

Now I am not sure where the £30k borehole costs come from, but my farming mate had a 60m one done for £1800.  They do a lot of drilling down here so even though it is often into granite, the local geology is well understood.

 

(I would not recommend a borehole system for most domestic properties)

Edited March 19 by SteamyTea

[jack]

5 minutes ago, SteamyTea said:

Now I am not sure where the £30k borehole costs come from

 

£30k was the total system cost, which was a guess on my part (added a bit to my vague memory of £20-25k for a typical slinky-type system).

 

Quick search found: https://www.greenmatch.co.uk/ground-source-heat-pump/borehole:

 

Quote

Ground source heat pump borehole cost

Ground source heat pump borehole costs will typically range from £10,000 – £30,000. This depends on the size of your home, which helps decide how many boreholes you need. 

 

Total costs might range from £25,200 – £53,000, considering the heat pump unit itself, and the additional installation jobs such as laying pipes and groundworks. 

 

Or https://www.imsheatpumps.co.uk/blog/ground-source-heat-pump-borehole-cost/:

Quote

The cost of installing a vertical GSHP

If we take the 12kW ground source heat pump, the total cost of installation can be around £25,000 – £30,000. Although again, this is just an estimated figure.

 

A study by the Department of Energy and Climate Change  found that installation costs comprise of 49% equipment and 51% non-equipment. Of the non-equipment costs, 60% of that is drilling boreholes. This is quite a chunk of the total installation cost. On the other hand, a 12kW horizontal system costs approximately £15,000 – £18,000.

 

Given your property has relatively low heating requirements, it'll be at the low end of that range, so probably around £25k.

 

You need to add to your numbers above the periodic replacement of the heat pump itself - maybe £10k every 10-20 years? Not sure. TBF, you probably need to replace an ASHP at least as often, but they are a lot cheaper.

 

Plus a few hundred quid every few years to replace the fluid.

[jack]

(PS: I'm going to stop replying on this topic, as we've hijacked the OP's thread)

[Iceverge]

19 hours ago, ElliotP said:

We're a the planning stage, and have appointed an architect. 

 

A great stage to start this thinking rather that 6 months down the line. 

 

19 hours ago, ElliotP said:

Budget wise I'm not looking to go all-out, it will be *relatively* tight,

 

Keep an eye on this. Shrink the house to fit your budget with sone contingency. There will come a day when you need to throw money at it to overcome some obstacle. 

19 hours ago, ElliotP said:

.  While I want to get close to passive haus standards, cost-benefit will be more important to me, such as not spending £50k in construction costs to gain thermal savings of £500 a year on heating for example

 

Passivhaus is designed to be an economic corner where the added efficiency gets rid of the need for a conventional central heating system. If it's costing £50k for £500 then you've done it wrong. 

 

Use the spreadsheets here to get a feeling for the balance of heating needs. 

 

Forget GSHP and battery's. Too dear Vs the benefit. 

 

Don't bother with the PIR internally. Just widen the cavity. Stainless steel ties are cheap enough. Use separate lintels for both leafs. 200mm cavities are the norm where I live. 

 

North facing glass is bad for energy efficiency. Careful with this. 

 

Airtighness is the lowest hanging fruit. It's a very big house, sub 1ACH should be very achievable. 

 

 

 

 

[jack]

21 minutes ago, Iceverge said:

Just widen the cavity.

 

... and find a way to make 100% sure that the insulation is installed properly. Pointless having a load of insulation in a wide cavity if there are gaps everywhere allowing for thermal bypass.

[ElliotP]

18 hours ago, nod said:

I would have perhaps started with your location and budget 

I found that using 70 mil insulated plasterboard dabbed directly onto the exterior walls has worked a treat on our previous build Hopefully does the same on our current build 

With three vaulted ceiling’s I’ve used 120 insulation between the rafters and taped them in multi foil 

Thank you all for your replies.  Location is South East. Right now there isn't a budget because I have no idea what to expect. I also plan to, if needed, draw this out over several years while the money comes in, doing what I can myself to complete it.  In my mind, circa £300k to get it watertight (foundations/slab/walls/glass/roof) would be amazing, but I have no idea if this is even close to realistic.   It's been 10 years since our last house when we built a sizeable extension, so my point of reference is some what out of date. 

 

3 hours ago, Iceverge said:

 

A great stage to start this thinking rather that 6 months down the line. 

 

 

Keep an eye on this. Shrink the house to fit your budget with sone contingency. There will come a day when you need to throw money at it to overcome some obstacle. 

 

Passivhaus is designed to be an economic corner where the added efficiency gets rid of the need for a conventional central heating system. If it's costing £50k for £500 then you've done it wrong. 

 

Use the spreadsheets here to get a feeling for the balance of heating needs. 

 

Forget GSHP and battery's. Too dear Vs the benefit. 

 

Don't bother with the PIR internally. Just widen the cavity. Stainless steel ties are cheap enough. Use separate lintels for both leafs. 200mm cavities are the norm where I live. 

 

North facing glass is bad for energy efficiency. Careful with this. 

 

Airtighness is the lowest hanging fruit. It's a very big house, sub 1ACH should be very achievable. 

 

 

 

 

 

GSHP - understood from all of the comments above to avoid.  I have about an acre of land I could install into, and I was going to buy and old digger and let my retired Dad loose on it for a few weeks, but by the sounds of it that still won't make up the price difference.  Batteries I already have 30kw  (got a pallet job lot from China a few years ago, so was cost effective).  

So generally no huge issue with going to a 200mm - 300mm cavity in terms of construction cost? Wider the better?  I must admit I would like to avoid PIR on the inside and keep the service void clear for... services. 
 

 

2 hours ago, jack said:

 

... and find a way to make 100% sure that the insulation is installed properly. Pointless having a load of insulation in a wide cavity if there are gaps everywhere allowing for thermal bypass.

Understood - I think the preferred method will be EPS beads pumped in, avoiding cavity batts. 

 

7 hours ago, SteamyTea said:

Do not deal with Seamus, he can causes loads of trouble.

 

I think that foundation system is a Kore one, which is pretty good.

 

I'm most likely going to be using a specific builder who is a family friend and who I have worked with before.  They are by no means knowledgeable in this area, but I'm aiming to provide the design/input and have them implement it (properly), which is why I'm trying to get an idea of what system to base the design from. The slab and the roof designs are what is troubling me the most at the moment, knowing which direction to go in.


 

Edited March 19 by ElliotP

[Dave Jones]

2 hours ago, ElliotP said:

Thank you all for your replies.  Location is South East. Right now there isn't a budget because I have no idea what to expect. I also plan to, if needed, draw this out over several years while the money comes in, doing what I can myself to complete it.  In my mind, circa £300k to get it watertight (foundations/slab/walls/glass/roof) would be amazing, but I have no idea if this is even close to realistic.   It's been 10 years since our last house when we built a sizeable extension, so my point of reference is some what out of date. 

 

 

GSHP - understood from all of the comments above to avoid.  I have about an acre of land I could install into, and I was going to buy and old digger and let my retired Dad loose on it for a few weeks, but by the sounds of it that still won't make up the price difference.  Batteries I already have 30kw  (got a pallet job lot from China a few years ago, so was cost effective).  

So generally no huge issue with going to a 200mm - 300mm cavity in terms of construction cost? Wider the better?  I must admit I would like to avoid PIR on the inside and keep the service void clear for... services. 
 

 

Understood - I think the preferred method will be EPS beads pumped in, avoiding cavity batts. 

 

I'm most likely going to be using a specific builder who is a family friend and who I have worked with before.  They are by no means knowledgeable in this area, but I'm aiming to provide the design/input and have them implement it (properly), which is why I'm trying to get an idea of what system to base the design from. The slab and the roof designs are what is troubling me the most at the moment, knowing which direction to go in.


 

 

QS QS QS

 

in lala land without it

[nod]

3 hours ago, ElliotP said:

Thank you all for your replies.  Location is South East. Right now there isn't a budget because I have no idea what to expect. I also plan to, if needed, draw this out over several years while the money comes in, doing what I can myself to complete it.  In my mind, circa £300k to get it watertight (foundations/slab/walls/glass/roof) would be amazing, but I have no idea if this is even close to realistic.   It's been 10 years since our last house when we built a sizeable extension, so my point of reference is some what out of date. 

 

 

GSHP - understood from all of the comments above to avoid.  I have about an acre of land I could install into, and I was going to buy and old digger and let my retired Dad loose on it for a few weeks, but by the sounds of it that still won't make up the price difference.  Batteries I already have 30kw  (got a pallet job lot from China a few years ago, so was cost effective).  

So generally no huge issue with going to a 200mm - 300mm cavity in terms of construction cost? Wider the better?  I must admit I would like to avoid PIR on the inside and keep the service void clear for... services. 
 

 

Understood - I think the preferred method will be EPS beads pumped in, avoiding cavity batts. 

 

I'm most likely going to be using a specific builder who is a family friend and who I have worked with before.  They are by no means knowledgeable in this area, but I'm aiming to provide the design/input and have them implement it (properly), which is why I'm trying to get an idea of what system to base the design from. The slab and the roof designs are what is troubling me the most at the moment, knowing which direction to go in.


 

300 k sounds very healthy to get to watertight I’ll watch with interest 

[MR10]

3 hours ago, ElliotP said:

 

 

I'm most likely going to be using a specific builder who is a family friend...


 

 

I'm assuming 'worked with before' was on a much smaller scale and detailing than required for this proposed build.

Thread carefully.

[gavztheouch]

Good luck! Im builidng a 210m2 shell for hopefully a similar budget of 300k. It should be doable depeding on how much work you do yourself.

 

Edit, I just reread your post and noticed you have a swimming pool triple garage and annex are these all inlcuded in your 300k budget. Minus the swimming pool I would budget around £600k to build the weather tight shell.

Edited March 19 by gavztheouch

[saveasteading]

3 hours ago, ElliotP said:

using a specific builder who is a family friend and who I have worked with before

 

Beware. Do you mind losing a friend?  Some things will go wrong. As long as you pay extra every time it is requested ( and happily so) then it could be OK.

[joe90]

I built brick and block with 200mm cavity, wall ties were not that expensive, I also used concrete lintels internally and brick arches externally so no cold bridging. You will read many threads here where attention to detail makes a big difference especially with airtightness (don’t let trades bore random holes in your membrane whatever it is).

[SteamyTea]

49 minutes ago, joe90 said:

don’t let trades bore random holes in your membrane whatever it is

Did you use a plastic VLC or did you parge coat? I can't remember.

 

I know you did something a bit novel around your window frames.

Edited March 19 by SteamyTea

[joe90]

54 minutes ago, SteamyTea said:

Did you use a plastic VLC or did you parge coat? I can't remember.

 

I know you did something a bit novel around your window frames.

Parse coat, cement render (even between floors) and plaster finish. Around windows and reveals was air proof foam and foaming glue (not a big fan of taped membranes).