Foundations??

[IanR]

9 minutes ago, lizzieuk1 said:

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??

 

I'm also on clay and due to the nature of my build didn't even go down that deep, but as I was converting a cow shed the top soil was already gone, I just cleared away the old floor and hardcore that was underneath. I actually had to build up the outside around my raft.

 

 

You need to clear away the top soil and any vegetation and as long as the clay you expose has > 100 kPa bearing capacity you can go from there. AFT can go lower than 100 kPa, but might need to change the build up. Top of the raft should be at least 150mm above ground level, but can be more.

 

Under the insulation is typically 150mm Type 1 plus 50mm layer of uncompacted pea gravel or granite chipping with no fines.

[lizzieuk1]

11 hours ago, IanR said:

 

I'm also on clay and due to the nature of my build didn't even go down that deep, but as I was converting a cow shed the top soil was already gone, I just cleared away the old floor and hardcore that was underneath. I actually had to build up the outside around my raft.

 

 

You need to clear away the top soil and any vegetation and as long as the clay you expose has > 100 kPa bearing capacity you can go from there. AFT can go lower than 100 kPa, but might need to change the build up. Top of the raft should be at least 150mm above ground level, but can be more.

 

Under the insulation is typically 150mm Type 1 plus 50mm layer of uncompacted pea gravel or granite chipping with no fines.

Thanks Ian,

 

Not had a test done yet so don't know the bearing capacity. Hopefully it will be suitable. 

 

With the raft needing to be 150mm about Ground level, is that standard for all rafts? Am thinking of how to grade the 2 levels - do you raise the hardstanding around the perimeter then grade down?

[IanR]

30 minutes ago, lizzieuk1 said:

Thanks Ian,

 

Not had a test done yet so don't know the bearing capacity. Hopefully it will be suitable. 

 

With the raft needing to be 150mm about Ground level, is that standard for all rafts? Am thinking of how to grade the 2 levels - do you raise the hardstanding around the perimeter then grade down?

 

It's a BC erquirement for DPC above ground. DPC/DPM will be at the top of the poured concrete of the raft. (unless you are building a partial basement)

[lizzieuk1]

4 hours ago, IanR said:

 

It's a BC erquirement for DPC above ground. DPC/DPM will be at the top of the poured concrete of the raft. (unless you are building a partial basement)

Yes, of course, was forgetting the dpc is directly on the raft top! 

[JohnMo]

6 hours ago, IanR said:

DPM will be at the top of the poured concrete of the raft

That then means the slab cannot be your finished floor and you have to screed? Which makes no sense. So surely the dpm would be below the concrete, not on top. As per sketch 

 

[lizzieuk1]

20 minutes ago, JohnMo said:

That then means the slab cannot be your finished floor and you have to screed? Which makes no sense. So surely the dpm would be below the concrete, not on top. As per sketch 

 

Yes, sorry I've caused confusion, what I meant was the dpm exits from under the concrete to finish level with the top of the concrete (as per your detail) not sure what happens under the Larsen truss though, does it have another dpc tied in or is the detail to minimise risk of water ingress between the insulation in the walls and the top of the raft insulation?(sorry I've not looked at TF details really so a bit ignorant on that aspect) 

[lizzieuk1]

Ooi how have others met the BC requirements for a level threshold? 

Was hoping to get level with garden paving but seems that's not an option with the raft design. 

[IanR]

As per image posted on page 2 of this thread

 

And in practice

 

2 hours ago, lizzieuk1 said:

Ooi how have others met the BC requirements for a level threshold? 

Was hoping to get level with garden paving but seems that's not an option with the raft design. 

 

At the threshold locally bring the outside surface up to the FFL with linear drain against the threshold if exposed, or just tip the surface away from the door a degree or two if there's an overhang above. Level thresholds are no problem with a raft.

 

 

Edited to add:

 

 

Edited February 27 by IanR

[lizzieuk1]

15 minutes ago, IanR said:

 

At the threshold locally bring the outside surface up to the FFL with linear drain against the threshold if exposed, or just tip the surface away from the door a degree or two if there's an overhang above. Level thresholds are no problem with a raft.

Is it possible to have a linear drain all round so that paving/patios can be level with FFL as well?

Just been reading about the detail for the door thresholds and wondering if that's possible all round 🤔 

[IanR]

5 minutes ago, lizzieuk1 said:

Is it possible to have a linear drain all round so that paving/patios can be level with FFL as well?

Just been reading about the detail for the door thresholds and wondering if that's possible all round 🤔 

 

I don't believe BC would accept it. Why do you want the outside ground at FFL level? What's your plan for the outside finish?

[lizzieuk1]

1 minute ago, IanR said:

 

I don't believe BC would accept it. Why do you want the outside ground at FFL level? What's your plan for the outside finish?

That's what I thought may be the case re bc.

I'm really thinking of how to integrate a patio that is at the same level as the FFL inside. We have an L shaped floor plan and will have sliding doors from both sides leading onto a patio so, ideally, would like it all on one level rather than stepped. 

I guess the rest of the perimeter can be stepped/sloped down and then the front & side doors can have sloping paths from ffl. 

[saveasteading]

On 26/02/2025 at 10:20, IanR said:

300mm EPS100 is about 2/3rds the cost of 200mm PIR, but EPS300 is required under ring beam + formers for edge section. Price should be similar, but, access to edge formers may come at a premium.

Rather late thinking this.

Are these comparable? Competitive prices from multiple manufacturers and merchants for a non load-bearing product  v a branded , specialised product.

 

Can anyone advise on the premium?

[Iceverge]

Nice plans. Not a lot I'd change really. 

 

If you build those bifolds as shown they'll loose as much heat as the rest of the house put together. They're very very drafty. 

 

I would opt for lift and slide windows or more French doors with fixed side panes. Be cautious of the window design too. Lots of transoms and mullions can look nice but loose a lot of heat vs a single pane. 

 

How committed are you to the woodstove? Do you have a free supply of timber and enjoy the process of preparing it?

I do, but yet we opted not to install one as the labour involved was troublesome having lived with one before. There's an air quality thing too ( internally and externally) which has been hashed to death on here so perhaps have a search if you're curious. 

 

I'm not a fan of parapeted copings on roofs. They will leak decades before a plain oversailing gable. 

 

Otherwise very nice layout and plenty of thought gone into it. 

 

 

If you husband can do that blocks will be a doddle. ( I can do blocks FFS and I'm trained in exactly nothing!)  What U value were you hoping to achieve for the walls?

 

 

[Iceverge]

1 minute ago, saveasteading said:

Rather late thinking this.

Are these comparable? Competitive prices from multiple manufacturers and merchants for a non load-bearing product  v a branded , specialised product.

 

Can anyone advise on the premium?

 

Online 350mm EPS70 is almost exactly the same price as 200mm PIR for the same U value. 0.11 W/m2K is £25. 

 

Seconds and co is £17 though.  It'd be £800 over a ground floor. Might buy a nice chair. 

 

 

 

[lizzieuk1]

9 hours ago, Iceverge said:

Nice plans. Not a lot I'd change really. 

 

If you build those bifolds as shown they'll loose as much heat as the rest of the house put together. They're very very drafty. 

 

I would opt for lift and slide windows or more French doors with fixed side panes. Be cautious of the window design too. Lots of transoms and mullions can look nice but loose a lot of heat vs a single pane. 

 

How committed are you to the woodstove? Do you have a free supply of timber and enjoy the process of preparing it?

I do, but yet we opted not to install one as the labour involved was troublesome having lived with one before. There's an air quality thing too ( internally and externally) which has been hashed to death on here so perhaps have a search if you're curious. 

 

I'm not a fan of parapeted copings on roofs. They will leak decades before a plain oversailing gable. 

 

Otherwise very nice layout and plenty of thought gone into it. 

 

 

If you husband can do that blocks will be a doddle. ( I can do blocks FFS and I'm trained in exactly nothing!)  What U value were you hoping to achieve for the walls?

 

 

Thanks Iceverge,

All really useful points.

 

Re the bifolds we've already decided to have large sliding doors instead, both for the point you raised and so we have a larger open viewpoint - realistically, with our weather,  they will be closed for much of the year anyway!!

 

The windows I think will be full panel with 'stuck on' bars (not my ideal but think far better thermally) we may well go with a more common 4 pane sash rather than 6 and certainly not 8. Need to research that a bit more though re thermal values, vacuum glass looks great but think still very expensive and looks only to be from timber sash companies, so, likely 3g instead as we'd prefer an aluclad type if possible, last build we had residence 9 in timber effect which we were quite  impressed with (upvc not alu but very nice & for bit cheaper I think)

 

We've had a stove for years and do love them, last build we had an external intake stove to protect the airtightness so will aim for that again and ensure a good seal for the flue outlet (no proper chimney stack, it will go straight out the wall in the 'mock' fireplace so will install pre-pour) we have quite a lot of trees round the farm so will have free wood for a fair while (and will plant more for future provision)

 

U value we are trying to get as low as reasonably/practically possible not firmed up yet but ?0.12?, possibly will use an external brick slip sheet with in built insulation if budget allows. Will use the ecobrix 365 which gives a good 0.15 value to start though.

 

Hear your thoughts on parapet roof, we had a lot of discussion about that,  but we love the style and it will be natural stone copings made by hubby (we're wanting to incorporate lots of stone detail as have moved from living our whole lives the Cotswolds so more an emotive choice rather than practical!)  we will have to concentrate hard on the detail for that to future proof it though! At least if we've built it we should know how to fix it in future!

 

Thanks for the positive re the layout, I did take a lot of time designing it to work for us as a family home and as a home that can work as the kids & us get older, really pleased with how it's turned out though, as usual, we will need to work hard on the budget and do lots and lots of the work ourselves (whole point of self build though I think!) 

 

[lizzieuk1]

On 26/02/2025 at 13:42, 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.

Do you think its possible to screw plasterboard directly to the woodcrete? Thinking if we parged externally then that could be an option internally as ideally don't really want a void between board & blocks (we would then chase services in - or at least try to, any thoughts on that?)

[Russell griffiths]

47 minutes ago, lizzieuk1 said:

Do you think its possible to screw plasterboard directly to the woodcrete? Thinking if we parged externally then that could be an option internally as ideally don't really want a void between board & blocks (we would then chase services in - or at least try to, any thoughts on that?)

Nope 

chasing services into woodcrete blocks is a non starter, it eats any form of cutting tool, if you go for a diamond disc it grinds the cement particles away but then sits there trying to burn through the wooden part. 
definitely re think this. 
as for screwing plasterboard onto woodcrete. 
I would say you need to go and visit a couple of woodcrete builds to decide your best approach. 
 

I’ve worked on two now and the surface finish to the blocks is nothing like flat enough to screw directly to. 
 

[Nickfromwales]

1 hour ago, lizzieuk1 said:

Do you think it’s possible to screw plasterboard directly to the woodcrete? Thinking if we parged externally then that could be an option internally as ideally don't really want a void between board & blocks (we would then chase services in - or at least try to, any thoughts on that?)

Parge for airtightness needs to be done internally as the porous blocks will allow airflow (infiltration) in at heads / footer / openings / top course etc, so you’ll need to detail this to the nth degree if you want the results. Just masses of extra hard work, plus your vapour permeability needs managing also so I’d stick to the standard methodology and stay away from creating more work for yourselves.

 

Chasing into woodcrete is something that the prison service should make inmates do. I promise you that crime rates would soon start dropping. 
 

You’ll need to surface mount cables, semi-recess deep electrical boxes, and dot n dab onto the blocks.

 

Ive done enough on all types of ICF projects to know what’s a good idea, an “OK” idea, and what’s a “feck that, never again” idea.

 

On one project the annex was done first, as a trial run for the builder, and that ended up with north of 30mm of bonding and plaster over the blocks. They tried to avoid dot n dab in there, I told them not too. Took months and months to dry out, and then hairline cracked EVERYWHERE.

 

I chased that (for my pipes and cables) with a 22mm SDS wood chisel, and that I had to re sharpen with a grinder every 20 mins.

 

After one or two walls you’ll be dragging your metal coffee cup along the bars of the cell.

[JohnMo]

1 hour ago, lizzieuk1 said:

ecobrix 365 which gives a good 0.15

If you include an unvented service cavity it come in at 0.14.

 

Work out where you need the airtight layer so it concedes with the ceiling, roof etc. then go from there. But inside is best as above. But your call.

 

22 minutes ago, Russell griffiths said:

I’ve worked on two now and the surface finish to the blocks is nothing like flat enough to screw directly to.

Airtight can be parge or membrane, battens can be packed out if needed to get straight vertical walls.

 

Advantage for doing all this internal, it's not weather dependent.

[IanR]

12 hours ago, saveasteading said:

Rather late thinking this.

Are these comparable? Competitive prices from multiple manufacturers and merchants for a non load-bearing product  v a branded , specialised product.

 

Can anyone advise on the premium?

 

By thickness EPS gives 60% of the thermal insulation that PIR does, so to achieve the U Value that 300mm EPS provides, you need 180mm PIR. I said 200mm PIR as I'd personally be buying that in 2 x 100mm sheets. When I cost compared for bulk order, I could get 100mm EPS100 sheets for half the price of PIR sheets and I was comparing BBA Certified EPS100 (load bearing) with an equivalent, but not load bearing, PIR.   Looking at what each are retailing for today it still seems to have the same price difference.

At the time (2016), and apparently still the case today, EPS formwork are not priced publicly by the various suppliers, but are offered as part of an Engineering & Supply bundle. For me prices varied widely between the companies offering such bundles and if the bundles included installation the incremental cost for installation was far higher than you'd expect to pay with local resource. The price I ended up paying, after looking at all options available, was the equivalent to paying around 10% more for the same m³ that I could purchase directly in sheet form, once I'd allowed a reasonable Engineering fee, so felt it not unreasonable as it included the EPS300 formers.

 

I can see the benefit of buying a full package: Engineering, supply and installation, especially if it also includes the house frame on top, as that totally de-risks that structural build, but, you have to expect that to come with a large premium attached, and you'll be paying that premium on everything, ie the insulation, steel, concrete, UFH and labour.

 

The best "full bundle" price I could get, including installation, was over 100% more than the price I paid using a local ground works company, PM'd by me, to install the Engineered raft by AFT, who supplied me the insulation from Springvale EPS.

 

[Iceverge]

3 hours ago, lizzieuk1 said:

vacuum glass looks great but think still very expensive and looks only to be from timber sash companies, so, likely 3g instead as we'd prefer an aluclad type if possible, last build we had residence 9 in timber effect which we were quite  impressed with (upvc not alu but very nice & for bit cheaper I think)

 

 

Vacuum glass is new on me. I must google it. 

 

I'm a big uPVC fan when it's done well. if it was more expensive more people would consider it. 

 

3 hours ago, lizzieuk1 said:

We've had a stove for years and do love them, last build we had an external intake stove to protect the airtightness so will aim for that again and ensure a good seal for the flue outlet (no proper chimney stack, it will go straight out the wall in the 'mock' fireplace so will install pre-pour) we have quite a lot of trees round the farm so will have free wood for a fair while (and will plant more for future provision)

 

Fair enough. What model are you considering. I thought Charnwood stoves were good when we were looking before I decided against it. 

 

 

3 hours ago, lizzieuk1 said:

U value we are trying to get as low as reasonably/practically possible not firmed up yet but ?0.12?, possibly will use an external brick slip sheet with in built insulation if budget allows. Will use the ecobrix 365 which gives a good 0.15 value to start though.

 

 

To be honest this has got wide cavity masonry wall written all over it. 

 

Brick facade. ✅

Sensible design with no silly overhangs, corner windows or upstairs walls held up by magic ✅

Desire for solid feeling wall ✅

Same airtightness precautions as ecobrix. ✅

 

 

Just copy the spec and details of this one and fit as much insulation as you can. I would be more than happy with good uPVC and SS wall ties however. 

 

https://passivehouse-database.org/index.php?lang=en#d_5319

 

 

There's far more savings to be had in a build via DIY in areas other than building the walls from ICF as concrete blocks and bricks are dirt cheap and a good mason will be very quick. Infact I reckon if you labour for the brickie/install install the batts then it'll be far more of a saving than DIYing the ecobrix. 

 

 

 

 

 

[saveasteading]

35 minutes ago, IanR said:

100mm EPS100

That's surprised me, being just 10% more.

What about the fancy perimeter eps former?

[lizzieuk1]

50 minutes ago, Iceverge said:

To be honest this has got wide cavity masonry wall written all over it. 

That may be so but we're not going down that route this time.

The last build we did we used 90mm kingspan (think porsche boxster in your walls just to pay for the tape!) as tighter site needed to avoid large cavity, along with lightweight 100mm blocks we achieved good u values but,  we had so many weeks lost with poor weather it was painful, not to mention grim on site in the rain as took so long to get watertight.

So many pros & cons with all the approaches so we can only weigh those up and go with what we're comfortable with.

[lizzieuk1]

56 minutes ago, Iceverge said:

What model are you considering. I thought Charnwood stoves were good when we were looking before I decided against it. 

We used a Panoramic last time - quite happy with those but, will certainly take a look at Charnwood to compare, thanks for the suggestion.

[lizzieuk1]

3 hours ago, Nickfromwales said:

Parge for airtightness needs to be done internally as the porous blocks will allow airflow (infiltration) in at heads / footer / openings / top course etc, so you’ll need to detail this to the nth degree if you want the results. Just masses of extra hard work, plus your vapour permeability needs managing also so I’d stick to the standard methodology and stay away from creating more work for yourselves.

 

Chasing into woodcrete is something that the prison service should make inmates do. I promise you that crime rates would soon start dropping. 
 

You’ll need to surface mount cables, semi-recess deep electrical boxes, and dot n dab onto the blocks.

 

Ive done enough on all types of ICF projects to know what’s a good idea, an “OK” idea, and what’s a “feck that, never again” idea.

 

On one project the annex was done first, as a trial run for the builder, and that ended up with north of 30mm of bonding and plaster over the blocks. They tried to avoid dot n dab in there, I told them not too. Took months and months to dry out, and then hairline cracked EVERYWHERE.

 

I chased that (for my pipes and cables) with a 22mm SDS wood chisel, and that I had to re sharpen with a grinder every 20 mins.

 

After one or two walls you’ll be dragging your metal coffee cup along the bars of the cell.

Thanks Nick, all interesting pointers. Looks like we need to parge inside and dot n dab which is fine. Hubby thinks he may just parge externally as well as we build up, we'll see how that pans out!  Used dot n dab on last build and quite understand the difference with speed of drying & cracking to wet plaster - def something I'm mindful of!

I'm not sure of Ecobrix have improved the uniformity of the blocks since they took over, will get a good look/question that when we pop over to the supplier.