Timber frame vs ICF vs Traditional masonry for a new build

[saveasteading]

I spot people with recent knowledge of foundations.

 

Our Engineer has designed something I think is suitable for forklifts. Any of you with timber frame able to copy or describe what you did for footings and floor slab?

 

ground bearing slab or raft? footings connected or separate? how much reinforcement?

sub-base/concrete /insulation / screed or simply  sub-base /insulation/ concrete?

 

Steel straps to hold the building down?

That sort of thing.

[Adam E]

I went with Scotframe their engineers specifies straps to slab, and soil investigation company and structure engineer specified raft foundation with enough steel to build a battle ship 

I was really interested is a insulated slabs as a few on hear have done but non of my professionals had worked with them so went with traditional. 

[Bitpipe]

The MBC passive slab detail is here - https://www.mbctimberframe.co.uk/passive-foundation/

 

They fix a timber soleplate to the perimeter of the concrete (DPM and airtightness fabric sandwiched below) and the frame panels attach to that.

[Thorfun]

  On 06/03/2022 at 18:11, Bitpipe said:

The MBC passive slab detail is here - https://www.mbctimberframe.co.uk/passive-foundation/

 

They fix a timber soleplate to the perimeter of the concrete (DPM and airtightness fabric sandwiched below) and the frame panels attach to that.

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although we didn't use MBC we did use TSD as our structural engineers and they designed our slabs the same way. the timber frame was fixed to the concrete slab or the coursing blocks if above the basement. I think they fixed the sole plate at 600mm centers iirc

[Bitpipe]

  On 06/03/2022 at 18:17, Thorfun said:

although we didn't use MBC we did use TSD as our structural engineers and they designed our slabs the same way. the timber frame was fixed to the concrete slab or the coursing blocks if above the basement. I think they fixed the sole plate at 600mm centers iirc

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We did not use MBC for foundation as like you we built a basement but same detail, we had a 200mm exterior basement wall that the soleplate and panels went on to and the structural gf was 18mm OSB web joists with a steel lattice to provide necessary point support for the frame above.

[saveasteading]

Sitting on polystyrene. Excellent.

And it hasn't sunk into the ground or blown away yet?

 

We have that sand as natural ground but the engineer wants us to dig it out and replace with type 1, then doubly reinforced slab, then insulation then screed. I might suggest that the extra cost comes off their bill, which will mean that they owe us.

[Thorfun]

  On 06/03/2022 at 18:35, saveasteading said:

Sitting on polystyrene. Excellent.

And it hasn't sunk into the ground or blown away yet?

 

We have that sand as natural ground but the engineer wants us to dig it out and replace with type 1, then doubly reinforced slab, then insulation then screed. I might suggest that the extra cost comes off their bill, which will mean that they owe us.

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yep. ours is on a mix of EPS300 and EPS100 depending on where the SE said to put it. just like @Bitpipe our basement slab is also on EPS300 with the walls built on that and coursing blocks on top that the soleplate is fixed to.

 

it's still standing but isn't finished yet and has only been up about 6 months so can't really give you a long term analysis.

 

for our above ground structures we had to dig 2m down to the bedrock and trench fill and then lay the EPS on that. obviously, all done to SE specifications.

 

I can highly recommend TSD if you want to investigate an insulated slab like the MBC design. but paying for more structural engineering might be a bitter pill to swallow

[Nick Laslett]

  On 31/01/2022 at 20:05, Happy Valley said:

We are building in ICF - polystyrene blocks. We have a builder.

 

…There is very little we would change - but one thing that would have made the whole build easier is designing the openings of the house (windows doors sliders) around the size of the blocks. There is a window which is right on a corner which is not ideal when cutting ICF corners. We would also get a structural engineer who understood ICF as ours has lots of rebar which the manufacturer deems unnecessary.

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Just to echo these points from Happy Valley. If you can adapt your design to fit the strengths of the ICF system it will make things much simpler. 

[saveasteading]

When questioned on the heavy construction we (not me unfortunately) were told uplift, down force, thrust.....all of which exist but i think are overestimated here. We will be asking for the calcs, and i will get the red pen warmed up.

Most glaringly is....remove 150mm of natural sand and replace with 150 type 1.....then put PIR on it before screed.  

Perhaps type 1 is the default and no further thought is given.

 

I'd most like to see either a standard drawing of a kit timber building onto a conventional edge footing, or photos of same.

 

[dpmiller]

standard trench fill for us, blocks on flat up from that, subfloors poured over blinded hardcore *inside* the blockwork. One course of block above that to FFL and TF kit nailed and strapped onto it. Pics in my build thread...

[Iceverge]

Here's a nice one. 

[Bitpipe]

  On 06/03/2022 at 18:35, saveasteading said:

Sitting on polystyrene. Excellent.

And it hasn't sunk into the ground or blown away yet?

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This is not flimsy packaging polystyrene  https://www.specifiedby.com/styrene-packaging-insulation-ltd/stylite-eps-geofill-void-formers/geofill-compressive-strength-factsheet_4eeaa0ea.pdf

 

We used 300mm EPS 200 blocks (1.2mx2,4m) for the slab which needed two people to place and were not going anywhere. Luckily we did not need to cut any as it was quite tough. The number relates to the compressive strength & the SE specced the grade. Was relieved as EPS 250 and EPS 300 were a lot more expensive.

 

200mm EPS 70 was used to clad the exterior basement walls, softer and easier to cut - as it sat under the cavity of the TF panels (to meet the insulation when pumped in) it did not need to be load bearing aside from resisting the basement backfill. 

 

 

[saveasteading]

  On 07/03/2022 at 12:51, Bitpipe said:

This is not flimsy packaging polystyrene

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No, of course not, but it is not concrete either.  Very impressive, and a benefit of the package process of joined-up thinking.

 

  On 07/03/2022 at 12:05, Iceverge said:

Here's a nice one. 

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What purpose do you think the bottom concrete has, other than tidyness?

[Bitpipe]

  On 07/03/2022 at 13:04, saveasteading said:

No, of course not, but it is not concrete either.  Very impressive, and a benefit of the package process of joined-up thinking.

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Concrete goes on top  - I was also worried they may blow or slide about and was considering pinning them to each other but they were 'king heavy and once down were going nowhere. 

 

Mine sat on 50mm of sand blinding the 150 compacted type 1 and the membrane sat on top of the EPS, dressed down at the sides. The concrete crew just built the slab on the top of all that. By luck, this EPS raft extended about 500mm beyond the edge of the slab without any trimming so there was a nice flat surface for the vertical EPS to sit on.

 

Cutting the EPS 70 was horrible, I used a small chainsaw and the inside of the basement was like a giant snow globe. 

[Nickfromwales]

  On 07/03/2022 at 13:04, saveasteading said:

What purpose do you think the bottom concrete has, other than tidyness?

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It is a bridge over the possibly unstable ground in between the trenches. A raft over trenches in essence. 
It also gives a uniform level platform for the insulation to sit on too. Not necessarily a problem with a poured floor / screed, but a nice surface to work from nonetheless. 
Ground conditions are everything with foundation designs so proposals will differ site to site. 

[Iceverge]

As @Nickfromwalessays it may be a structural requirement. It does make it easy to lay radon barriers/ DPM and makes the builders life easier during the build. 

 

In this case assuming the ground is ok it may have been done because of the polished concrete floor. This pour could have been left very late in the build, reducing the chance of damage and being able to tightly control the concrete curing to avoid cracks. 

 

Another possible cause is that's it's a hangover from the days of drafty fossil fueled houses that need an intermittent quick response heating system. There's still loads of people employing <100mm screed without giving a thought to this. 

[Nickfromwales]

Have many on here had comparative costs to go from a regular foundation system ( block and beam over trench or the type of system linked a few posts back ) vs a passive raft ( assuming screw piles are not required in each instance )? 

[saveasteading]

  On 07/03/2022 at 14:28, Nickfromwales said:

passive raft

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By 'passive raft', does this mean a slab to the passive house principles? 

ie not a structural raft which is supporting the superstructure. I say this as the slabs in the pictures appear to be fairly slender, and have crack-control mesh, not structural.

[Bitpipe]

  On 07/03/2022 at 15:15, saveasteading said:

By 'passive raft', does this mean a slab to the passive house principles? 

ie not a structural raft which is supporting the superstructure. I say this as the slabs in the pictures appear to be fairly slender, and have crack-control mesh, not structural.

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It is a structural raft and forms the entirety of the foundation.

 

There is additional thickness & strengthening around the perimeter and where the point loads of the structure above require it.

 

The EPS acts as formwork and insulation, it is specced to take the load of both the slab and structure above without deformation.

 

Additional benefit is that the UFH pipes are tied to the mesh and therefore the traditional 'on slab' insulation & screed is not required. 

 

Some have been able to power-float the slab post pour and use that as the finished surface.

[saveasteading]

  On 07/03/2022 at 15:37, Bitpipe said:

a structural raft

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Thanks, just checking terminology, as 'raft' to me is a thickish  slab with 2 layers of heavy reinforcement.

 

Yes, tying the UFH  down to mesh is a bonus....once had a plumber insist on pouring his own screed and it got under the PIR which floated.

[Bitpipe]

  On 07/03/2022 at 15:50, saveasteading said:

Thanks, just checking terminology, as 'raft' to me is a thickish  slab with 2 layers of heavy reinforcement.

 

Yes, tying the UFH  down to mesh is a bonus....once had a plumber insist on pouring his own screed and it got under the PIR which floated.

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The substrate does need to meet a certain spec also - many here had to provide a suitable bed of, for example, washed railway ballast and quarry dust, the EPS can't just sit on the subsoil.

 

Given the house above will be passive and have a very low space heating requirement, the whole slab acts as a single zone and does not need a fast response time like traditional UFH. Also gives option, if ASHP is used, to cool slab in summer.

[Simplysimon]

  On 06/03/2022 at 18:35, saveasteading said:

We have that sand as natural ground but the engineer wants us to dig it out and replace with type 1, then doubly reinforced slab, then insulation then screed. I might suggest that the extra cost comes off their bill, which will mean that they owe us.

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most of our ground is clay, however, where the house sits there is an outcrop of whin not far under the surface. bc wanted us to dig it out to replace it with concrete until we had a discussion and made them see sense. strip founds and beam and block here.

[IanR]

Ground-bearing insulated raft for me also.

 

 

The sole-plate was sealed to the slab with a non-curing butyl sealer and bolted down. The loads from my internal load-bearing walls were just low enough to have avoided internal beams, however we still included them to stabilise the raft and remove any risk of it curling up as it cured. The internal beams were 200mm thick, and the integral perimeter ring beam was 300mm. The majority of the raft is 100mm thick with 300mm of EPS100 under. The UFH was stapled to the EPS with A193 mesh over the top.

 

With a light-weight super-structure I didn't need the external, separate ring beam for strength, but it removed all thermal bridges. If I did it again I'd avoid this extra detail and small gain it delivers.

 

The raft sits on 40mm of pea shingle over 160mm of compacted Type I, directly on to clay.

 

A few pictures:

 

I went with a power-floated finish as I planned a 4mm thick poured resin floor finish directly over the top for the living areas.

 

 

[redtop]

Well we had 47 piles, concrete caps then steel posts, steel ring beams and then timber frame up from that. House sits at 300mm of the ground one side to 2.5m the other, thats over a distance of about 6m max so its on a pretty steep slope with trees all round.

 

Edited March 7, 2022 by redtop

[saveasteading]

Thanks all. Confirming what I knew really.

This is conservative for a 6m span timber  building with no upper floor and a central prop.

Especially as it requires us to dig out the strong sand base and replace with type 1.

Bottom slab is shown as 125 thick with 2 layers A252

Edge beam 2no layers of B1131 and pairs of 12mm links at 300cc.