Hello ​👋​​👋​

[Tim_C]

Hi everyone - I'm Tim

 

Newbie selfbuilder here, in the early stages of planning our self-build project in South Wales (But currently living in Bristol). Looking to build a family home to passive house principles, and avoid any Grand-designs style crises during the process!

 

Excited to be part of this forum, which is a great source of info! I look forward to picking your collective brain more as we make our design choices and progress with the project. 

[Dreadnaught]

Welcome. @Nickfromwales comes from down the coast in Wales.

[Nickfromwales]

4 hours ago, Tim_C said:

Hi everyone - I'm Tim

 

Newbie selfbuilder here, in the early stages of planning our self-build project in South Wales (But currently living in Bristol). Looking to build a family home to passive house principles, and avoid any Grand-designs style crises during the process!

 

Excited to be part of this forum, which is a great source of info! I look forward to picking your collective brain more as we make our design choices and progress with the project. 

Hi and welcome.
 

Glad you're not looking to bother with the PH cape and matching slippers, as you probably need to live 1.5x to get all that extra bother and cost back.

 

Timberframe or ICF or other in mind? 

[Tim_C]

54 minutes ago, Nickfromwales said:

Hi and welcome.
 

Glad you're not looking to bother with the PH cape and matching slippers, as you probably need to live 1.5x to get all that extra bother and cost back.

 

Timberframe or ICF or other in mind? 

 

Thanks for the Welcome!

 

Potentially both Timberframe and ICF.

 

The plot is sloping, so needs a lower ground floor which dug into the hilside and partially below ground level. Working assumption at the moment is a raft foundation, tanked ICF lower ground floor then timber frame 1st/2nd floor. Definitely would be interested to hear if anyone on the forum has experience of this, given it's less common.  

 

 

 

 

[Nickfromwales]

5 minutes ago, Tim_C said:

 

Thanks for the Welcome!

 

Potentially both Timberframe and ICF.

 

The plot is sloping, so needs a lower ground floor which dug into the hillside and partially below ground level. Working assumption at the moment is a raft foundation, tanked ICF lower ground floor then timber frame 1st/2nd floor. Definitely would be interested to hear if anyone on the forum has experience of this, given it's less common.  

Quite a few on here have done basements by a 3rd party, and then plonked a TF atop, as most TF companies won't touch a basement (or anything sub / semi-subterranean) with a shitty stick.

 

May be a lot simpler for you to go with ICF all the way, but with timber for posi joists / internal walls etc. One point of contact for responsibility / coordination / liability, reducing risk massively (and avoiding errors and the blame game).

[saveasteading]

I've done a few buildings ( schools and factories) on steep slopes.

My principle has been to build a platform at the higher level, then a conventional framed building on top.

That keeps it simple and vastly more economical.

No basement as you get into a different level of complexity and risk.( digging into the ground, waterproofing, stability, access)

So that is conventional strip footings ans walls up to level . Then beam and block or precast planks make the surface. You are then out of the ground and on a solid surface.

 

With a raft you have a big hole to dig then work in. If the slope is steep there is potential differential movement of the ground.

 

If the slope is extreme then you can perhaps have a natural extra storey or part of one.

 

Worth mentioning perhaps that in a couple of those jobs the original designers had assumed the dig and raft technique or retaining walls and mass fill to make a platform.  I met one during negotiation and discussed  the principles, and he was simply surprised at the cost difference, not being a contractor.

 

Beam and block then a conventional kit above is my suggestion.

[JohnMo]

Our site is also sloping original plan was to build-up the front of house to level. In the end we moved the hill about to make a flat area for the house. Ended up way easier. Man with big digger for a few weeks was cheap enough. Or do as @saveasteading - basements and underground working no thanks. All the cost unknowns are below finished ground level, so avoid to much work there.

 

Also we built from ICF - don't see any value adding a timber frame on top, just keep going with ICF.

[saveasteading]

Of course it matters massively where your doors are, to walk out onto land or mid-air.

[Mr Punter]

10 hours ago, Tim_C said:

tanked ICF lower ground floor

 

If you go with semi basement ICF you will need as a minimum type C waterproofing, which involves a profiled drainage sheet on the walls and floor, a drainage channel formed in the floor perimeter, a sump with a high level alarm end a pump.  You also  have to consider where you locate insulation and how you deal with drainage.  Warranty providers may suck air through  their teeth.

 

Far better, if the site allows, change the profile of the land and have your building above ground, even if you need some retaining structures in the garden / drive.

[ToughButterCup]

Welcome.

 

13 hours ago, Tim_C said:

...

The plot is sloping, so needs

...

 

How much of a slope? 

A gentle slope is a massive advantage.

1 in 1 , not so much.

We used about 2000 (ish)  tonnes of MoT1 and other stuff ( dig-out from elsewhere) to make the raft sit 'comfortably'   

 

Tell us about your slope please!

 

Ian

[saveasteading]

2 hours ago, JohnMo said:

Our site is also sloping 

If I recall, you are on sand which is very free draining and not seasonally affected.

It would be different on clay.

[JohnMo]

13 minutes ago, saveasteading said:

If I recall, you are on sand which is very free draining and not seasonally affected.

It would be different on clay.

You are correct. But either way wouldn't be doing a build part underground, if I had any other options. Too many variables to start costing you big money.

[Tim_C]

7 hours ago, ToughButterCup said:

 

How much of a slope? 

 

 

Slope is about 1 in 6

 

Appreciate everyone's comments. We're definitely striving for simplicity - doing more earthworks and building a beam&block platform to sit a TF on top definitely sounds appealing. We'll investigate!

[Nickfromwales]

1 hour ago, Tim_C said:

 

Slope is about 1 in 6

 

Appreciate everyone's comments. We're definitely striving for simplicity - doing more earthworks and building a beam&block platform to sit a TF on top definitely sounds appealing. We'll investigate!

If you go for a block and beam foundation then you'll need a clear perimeter all around the slab, to get the required cross ventilation. This may then provoke a retaining wall £££.

[JohnMo]

1 hour ago, Tim_C said:

Slope is about 1 in 6

That is pretty flat, our house is around 10m at the deepest and 7m for most of it. So that would be only 1.5m buildup at the most. Ours was a 1:1 slope.

[Nickfromwales]

23 minutes ago, JohnMo said:

That is pretty flat, our house is around 10m at the deepest and 7m for most of it. So that would be only 1.5m buildup at the most. Ours was a 1:1 slope.

I'm just about to start a new build for a new client and the site was a bit of an odd-ball, with the rear left quarter needing 'attention' according to the geotechnical report, before we could build a raft and a new ICF structure atop. I made the call to drop grade by 500mm, with the added benefit of slightly higher internal ceiling heights but no affect on ridge height, which cured a problem with some beneficial side effects.

 

Sometimes you can turn issues into advantages, so a sloping site doesn't always mean a headache!

[saveasteading]

On 13/07/2026 at 21:47, Nickfromwales said:

clear perimeter all around the slab, to get the required cross ventilation

It's usually possible to use pipes in periscope form where the airspace is facing ground.. Takes some thinking through. But it is only the high face and a small length of each side.