Foundations??

[IanR]

8 minutes ago, lizzieuk1 said:

Thanks Ian. That's hugely helpful, I'm wondering if I should reach out to some of the raft suppliers and get some high level estimates.

 

Definitely, at the very least you'll be better informed when discussing with your own SE.

 

If you can, break Engineering and Supply away from installation. My experience was that when the bundle included the installation as well the premium went up even further.

Edited February 26 by IanR

[Nickfromwales]

1 hour ago, lizzieuk1 said:

Thanks Ian. That's hugely helpful, I'm wondering if I should reach out to some of the raft suppliers and get some high level estimates.

If it’s only the time and cost of the enquiries then seems a wise decision.

 

I’d go for the raft every day of the week, much better to have the UFH in the constructional slab like a big storage heater, but check if you need props etc to hold the walls during construction of the ICF as you then can’t drill and fix into the floor. 
 

I’ve said my 2-penneth on here about woodcrete ICF vs EPS, but if you’re not going for airtight and MVHR you’ll be fine. If you are (which would be my first and most important advice / recommendation) then you’ll need to know what hoops to jump through to seal the woodcrete blocks as required. 
 

Which block manufacturer have you opted for? 

[IanR]

5 minutes ago, Nickfromwales said:

but check if you need props etc to hold the walls during construction of the ICF as you then can’t drill and fix into the floor. 

 

This is a good point. You may need to design your UFH around how you need to prop the ICF. Would need some robust oversight during the build phase.

 

7 minutes ago, Nickfromwales said:

I’ve said my 2-penneth on here about woodcrete ICF vs EPS, but if you’re not going for airtight and MVHR you’ll be fine.

 

I was wondering when to bring this one up...

[Nickfromwales]

18 minutes ago, IanR said:

This is a good point. You may need to design your UFH around how you need to prop the ICF. Would need some robust oversight during the build phase.

My foundation and ICF ‘guy’ laid 2 lots of 18mm OSB and braced with timbers to make a platform to fix down into without breaching the slab. Was a bit of extra work for sure, but everything is “doable”. 
 

20 minutes ago, IanR said:

I was wondering when to bring this one up...

You know me, lol, I’m never one to start a fight….

 

“In the red corner we have EPS, and in the blue corner we have Woodcrete”. Round 1, ding 🛎️ 🥊, 🤣

[JohnMo]

53 minutes ago, Nickfromwales said:

Woodcrete

Round 1

Woodcrete - No floor drilling needed, not a single hole made in my finished floor during wall construction. All bracing was OSB directly screwed to blocks. Then removed 24 hrs later. Zero risk of ufh pipe damage.

 

Airtight either parge, purple spray airtight stuff or membrane - all easy enough. More work than EPS.

[lizzieuk1]

2 hours ago, Nickfromwales said:

If it’s only the time and cost of the enquiries then seems a wise decision.

 

I’d go for the raft every day of the week, much better to have the UFH in the constructional slab like a big storage heater, but check if you need props etc to hold the walls during construction of the ICF as you then can’t drill and fix into the floor. 
 

I’ve said my 2-penneth on here about woodcrete ICF vs EPS, but if you’re not going for airtight and MVHR you’ll be fine. If you are (which would be my first and most important advice / recommendation) then you’ll need to know what hoops to jump through to seal the woodcrete blocks as required. 
 

Which block manufacturer have you opted for? 

Thanks Nick.

We're going with Ecobrix (Durisol) have researched for quite some time now and feel that fits our needs/wants best, have a supplier very nearby so can tap them for advice etc. Pro is no props needed but Yes, aware of the air tightness needs - we will likely parge coat externally & wet plaster internally, warm roof with loft rooms likely easi joist with blown cellulose but still researching that. Def will be having mvhr so vital we get the air tightness correct. Managed a 4 on our last build so did OK- block & stone with dot n dab- and LOTS of foam! No mvhr on that one though. Aiming for far better on this one though (def under 3).

[lizzieuk1]

39 minutes ago, JohnMo said:

Round 1

Woodcrete - No floor drilling needed, not a single hole made in my finished floor during wall construction. All bracing was OSB directly screwed to blocks. Then removed 24 hrs later. Zero risk of ufh pipe damage.

 

Airtight either parge, purple spray airtight stuff or membrane - all easy enough. More work than EPS.

Thanks JohnMo, lots of great info from you that has really helped us. 

Will probably go for a parge coat, ooi did you wet plaster?

[ToughButterCup]

4 minutes ago, lizzieuk1 said:

...

We're going with Ecobrix (Durisol)

...

 

Almost recovered from our Durisol Trauma. I'm up for looking at your build ... when do you start?

[lizzieuk1]

1 minute ago, ToughButterCup said:

 

Almost recovered from our Durisol Trauma. I'm up for looking at your build ... when do you start?

Lol, seems any build is traumatic! We don't have a start date yet, already living on site in the old house (5 of us playing sardines!)

Would be very happy for ypu to take a look.

[ToughButterCup]

1 minute ago, lizzieuk1 said:

....

Will probably go for a parge coat, did you wet plaster?

 

I parged out AND in , and then wet plastered inside as well. Why - in  AND out? Because I didn't know any better, and because I'm on my own - so don't (didn't) have the research time.

Skim-reading is deadly sometimes.😔

1 minute ago, lizzieuk1 said:

Lol, seems any build is traumatic! We don't have a start date yet, already living on site in the old house (5 of us playing sardines!)

Would be very happy for ypu to take a look.

 

PM me when the time comes - 

[lizzieuk1]

1 minute ago, ToughButterCup said:

 

I parged out AND in , and then wet plastered inside as well. Why - in  AND out? Because I didn't know any better, and because I'm on my own - so don't (didn't) have the research time.

Skim-reading is deadly sometimes.😔

 

PM me when the time comes - 

😬 Well I guess that ensured a great air test result! 

Will let you know once we're ready to go 👍

[JohnMo]

23 minutes ago, lizzieuk1 said:

parge coat externally & wet plaster internally

You only need one or the other.

 

I did parge then 50mm service battens screwed through parge into woodcrete and dry lined (jointed plasterboard). Also provided an OSB area at top of wall for all wiring to clip to.

 

Parge coat gave zero air leakage via wall. Had big air leakage to fix at DPC, used liquid membrane for that. If plastering direct the air leakage is likely where you have cables and sockets, so some thought needed.

[saveasteading]

4 hours ago, IanR said:

An insulated raft doesn't need to cost more

Thanks for your summary. 

I feel it is a tiny bit biased towards expecting a raft to be better value. I confess to having the contrary expectations.

Also that I would expect to PM myself,  using fairly ordinary local builders.  That is a lot of value.20% of more.

 

To tweak yours.

300mm eps = 150 pir as insulation. Similar cost. Less dig pir.

Raft needs 2 layers of heavy ish steel, compared to 1 layer of the lightest.

Raft has a deepened perimeter snd at walls.

Raft is poured in the weather. That's a risk. With my contractor hat I don't like delay or risk.

The detailing for insulation is standard and easy. Of course raft people say otherwise.

 

Now. I was a professional estimator for yonks.  I'd rather fancy doing a roper cost comparison but haven't the time. 

Gut feeling. 20% more for a raft. Maybe 30%.  Justifiable if not PMing it.

 

As for trees. I quickly looked at the tree tables but couldn't see hawthorn. 

The nearby  founds will be no deeper than 1.2m, the rest at 1m, i'm pretty sure.

Forget piling too. It won't be necessary.

 

Other people can advise. Are there any special measures to protect the eps at the perimeter or for the interface to the walls above?

[IanR]

30 minutes ago, saveasteading said:

Also that I would expect to PM myself,  using fairly ordinary local builders. 

 

I used local ground works (it's what took most of the cost out of the full bundled price), but they did have experience with warehouse rafts.

 

30 minutes ago, saveasteading said:

I feel it is a tiny bit biased towards expecting a raft to be better value.

 

...and it thought I was being vary fair. Here's why:

 

Tweaked again:

300mm eps = 200 pir as insulation. Similar cost. same dig as no screed

Optimised insulated Raft needs just 1 layer of the A142 mesh. 

Raft has a shallower perimeter at walls than a strip foundation - less dig, less muck away

Raft is poured in the weather. That's a risk. - Yep there's a risk, not sure how much more than collapsing trenches in the rain. Both should really adjust timing to suit weather.

 

30 minutes ago, saveasteading said:

The detailing for insulation is standard and easy. Of course raft people say otherwise.

 

Is that regarding thermal bridging? - I think we may be saying the same thing. Extra insulating material to break the walls from the heat sink strip foundations. It can be mitigated to a reasonable extent, but at extra cost not required on an insulated raft.

 

30 minutes ago, saveasteading said:

Gut feeling. 20% more for a raft. Maybe 30%.  Justifiable if not PMing it.

 

Rather than gut feeling, where's that extra cost coming from, have I missed some costs from the list? I'm assuming PM'ing is the at same cost for each, ie. DIY or local groundwork team. There's nothing tricky with an insulated raft, as long as they can read a drawing.

Edited February 26 by IanR

[lizzieuk1]

2 hours ago, JohnMo said:

You only need one or the other.

 

I did parge then 50mm service battens screwed through parge into woodcrete and dry lined (jointed plasterboard). Also provided an OSB area at top of wall for all wiring to clip to.

 

Parge coat gave zero air leakage via wall. Had big air leakage to fix at DPC, used liquid membrane for that. If plastering direct the air leakage is likely where you have cables and sockets, so some thought needed.

Was there a reason you didn't parge the outside? Am thinking that way the entire envelope is airtight and you can chase services/fixings in without worry internally.

[IanR]

5 minutes ago, lizzieuk1 said:

Was there a reason you didn't parge the outside? Am thinking that way the entire envelope is airtight and you can chase services/fixings in without worry internally.

 

You do need to pick one side or the other as the airt tightness side, and detail your roof structure into it. But I do like an external air tight layer, there are many fewer penetrations and no need for service voids, unless putting plumbing in the external wall. I have my air tightness layer on the outside of the structure and it worked well for me, although mine is timber-framed.

 

[TheMitchells]

Great information again from BuildHub!  Can we all get an invite to come and look?  I think 'Open days' at builds taking place with discussions about methods, would be fantastic learning opportunity. 😀

[JohnMo]

48 minutes ago, lizzieuk1 said:

Was there a reason you didn't parge the outside? Am thinking that way the entire envelope is airtight and you can chase services/fixings in without worry internally.

You would choose one airtight pathway, inside for me was way easier. Ceiling membrane draped onto wall and airtight glued in place. But I have all vaulted ceilings.

 

Air can move in all directions, if you do two airtight pathways for walls, you need to do that on the roof also, or you are just wasting time and money. Doing 2 is waste of time and money anyway. Choice inside or outside and stick with it.

[saveasteading]

3 hours ago, IanR said:

Rather than gut feeling, where's that extra cost coming from,

I think I need something clarified.

Are you classing a groundbearing slab as a raft? It isn't reinforced , as there is no bending, and only has crack control mesh.

Warehouse slabs are not rafts. They are usually uninsulated because they have heavy loading and an unheated, or reduced heat,  space. 

 

I am suggesting a very simple slab on the ground. No reinforcement needed but I would add the minimum.

Then the insulation of your choice :  actually I have a hunch towards 100mm eps with 100 pir staggered over it.

 

Gut feeling again, but based on many decades of prior thought and prejudice, plus stuff picked up on BH.

[IanR]

49 minutes ago, saveasteading said:

Are you classing a groundbearing slab as a raft? It isn't reinforced , as there is no bending, and only has crack control mesh.

 

No, I'm referring to an Insulated Raft. And while there are many terms used for it, it's the one most often used here and by the Engineers that Engineer them.

 

A "raft" as it supports the full weight of the building. ie. all walls including external and internal load bearing walls*** sit on and pass their loads through it to the ground beneath, rather than a floor slab that sits between the load bearing walls.

 

49 minutes ago, saveasteading said:

I am suggesting a very simple slab on the ground. No reinforcement needed but I would add the minimum.

Then the insulation of your choice :  actually I have a hunch towards 100mm eps with 100 pir staggered over it.

 

Then we're not comparing like-for-like. If you only want Building Regs performance, then standard foundation details would be the way to go, although 100mm EPS isn't going to achieve it. To meet the same U Value as a typical Insulated Raft then 200mm PIR would be required over a floor slab. But that still won't match the raft for psi (Ψ) values, further mitigation would be required.

 

Insulated Rafts become economical when wanting higher thermal performance from your building.

 

As an example (not mine), publicly available from https://www.advancedfoundationtechnologylimited.co.uk/projects/paul-williams/   For close to Passivhaus performance, or PH performance when combined with a Larsen-truss wall structure.

 

This requires only a 450mm dig depth, if that's sufficient to clear the organic matter.

 

 

 

***sometimes with an additional, unconnected or partially connected ring beam for an external skin for Passivhaus performance

 

Ref. https://www.advancedfoundationtechnologylimited.co.uk/our-products/passive-building-foundations/

Edited February 26 by IanR

[Iceverge]

Great discussion this. 

 

Welcome @lizzieuk1. Sounds like a nice project. Do you have any plans to share? Without your name location etc of course. 

 

Different designs are more suited to different build methods, even on the same site..

 

Moving more concrete inside your thermal envelope isn't  going to make your house better. Even the slab perimeter bridging detail isn't the biggest issue. Airtightness is really everything in a low energy house. 

 

Regarding woodcrete ICF it is much the same as masonry regarding airtight measures. As your hubby is a mason I think blocks are the logical choice. Passivhaus is easily possible and quite economical with masonry but requires some thought. Our actual heating demand is about 17kWh/m2 per annum. 

 

 

 

 

 

 

 

[Iceverge]

Separately on the raft Vs strip foundation detail I think theoretical and individual examples aren't representative of the broad reality of building.

 

As I remember @IanR was a specific case. A client with great knowledge and motivation and a very very large slab.

 

On the whole you're dealing an industry that doesn't like thinking much. ( Buildhub is gladly a shining exception) Even though there's no technical reason for an insulated raft to be more expensive you're likely to be met with extra charges for forcing some long dormant brain cells into action. 

 

The overall best method is likely to be whatever is being used on local production building sites but slightly adapted to deliver high performance.

 

That's what we did, strip foundations and a concrete slab. We extended the insulated cavity below the floor insulation, (the GBS DenbyDale detail), included some extra floor insulation and put some GRP thresholds in. 

 

Over all nothing that scared the builders so no added cost but still a high performance floor. 

 

 

 

 

[lizzieuk1]

1 hour ago, Iceverge said:

Great discussion this. 

 

Welcome @lizzieuk1. Sounds like a nice project. Do you have any plans to share? Without your name location etc of course. 

 

Different designs are more suited to different build methods, even on the same site..

 

Moving more concrete inside your thermal envelope isn't  going to make your house better. Even the slab perimeter bridging detail isn't the biggest issue. Airtightness is really everything in a low energy house. 

 

Regarding woodcrete ICF it is much the same as masonry regarding airtight measures. As your hubby is a mason I think blocks are the logical choice. Passivhaus is easily possible and quite economical with masonry but requires some thought. Our actual heating demand is about 17kWh/m2 per annum. 

 

 

 

 

 

 

 

Thanks Iceverge.

 

The discussion certainly has brought lots of things to light! All really helpful though. 

 

Hubby is a stonemason but not a brickie - big difference- his main skill set is in carving architectural stone such as church door surrounds, window cills etc but, he can build a straight, level block wall and has the skills to work to tolerances etc. Hence the woodcrete as it is an easier diy option than block but offers what we want, not perfect by any means but we have to weigh the pros & cons. 

We're pretty on top of the airtightness issues, dealt with those on previous build so a good idea of where we need to focus our effort.

 

Will see if I can post our plans with redacted info. 

[lizzieuk1]

2 hours ago, Iceverge said:

Great discussion this. 

 

Welcome @lizzieuk1. Sounds like a nice project. Do you have any plans to share? Without your name location etc of course. 

 

Different designs are more suited to different build methods, even on the same site..

 

Moving more concrete inside your thermal envelope isn't  going to make your house better. Even the slab perimeter bridging detail isn't the biggest issue. Airtightness is really everything in a low energy house. 

 

Regarding woodcrete ICF it is much the same as masonry regarding airtight measures. As your hubby is a mason I think blocks are the logical choice. Passivhaus is easily possible and quite economical with masonry but requires some thought. Our actual heating demand is about 17kWh/m2 per annum. 

 

 

 

 

 

 

 

Hopefully this works! Plans. Should add there will be a 2nd floor in roof space as wellplans.pdfplans.pdf

Edited February 26 by lizzieuk1
Extra info

[lizzieuk1]

3 hours ago, IanR said:

This requires only a 450mm dig depth, if that's sufficient to clear the organic matter.

 

 

 

***sometimes with an additional, unconnected or partially connected ring beam for an external skin for Passivhaus performance

This would be a great start if we could get away with a 450mm dig and 150mm type 1, not sure we will on deep clay??