Selfbuild Experiment

[Zak S]

4 minutes ago, Gus Potter said:

Hi Zak S.

 

Yes that looks pretty soft right enough at certain depths. Looking at the cores the ones to the right seem to be from the surface, the left ones in the photo from greater depth? The shallower cores look like there is maybe a stiffer crust with soft clay below and that the bungalow founds are using this crust to spread the load out before it reaches the softer clays...

 

The folk that designed the founds for the bungalow may have taken advantage of this crust. I would still expore the raft first. If the water table is high and not likely to drop then the soft clay can't shrink as it will always be submerged. It also can't go anywhere.. it is confined at depth. Once you go down a bit the pressures in the ground from a raft are often found to be very modest so even a soft clay can carry a surprising amount of load with acceptable settlement.

 

 

Yes you guessed correctly. The one on the right was very wet though due to high water and a bit sandy. I suppose the water level will go up and down depending on the season as tree come back to life in summer and then in winter go to hibernate. Raft is definitely an option I am looking at alongside Ring and Beam with Blockbeam floor but would prefer RAFT with Void if that works.

[Gus Potter]

Yes the raft with a void is an option not least as it provides a service space under the floor. Have done some jobs this way.

 

On the technical side if you find a ground bearing raft is loading up the ground just a little too much then the weight of muck you dig out to create a void reduces the loading on the soil and bingo! it all works out.

 

 

 

 

[Zak S]

2 minutes ago, Gus Potter said:

Yes the raft with a void is an option not least as it provides a service space under the floor. Have done some jobs this way.

 

On the technical side if you find a ground bearing raft is loading up the ground just a little too much then the weight of muck you dig out to create a void reduces the loading on the soil and bingo! it all works out.

 

 

 

 

Hi. Thanks. Are you SE or ground work engineer?

[Gus Potter]

Got to the age where you dabble in all sorts, realised there are folk that have forgotton more than you know, hence enjoy being on build hub, every day is a school day here for me.

 

Keep up with the research Zak.

 

 

[epsilonGreedy]

@Zak SYou need to go back to the beginning and ask some fundamental questions.

1. When you purchased your plot with a large 180 sqm bungalow, what proportion of the plot value was for the building? Is it habitable? For example if the property cost £350k then it is likely the market value was assessed as £200k for the plot plus £150k for the building in need of £50k of upgrades.
2. Why do you want to spend serious money demolishing this large structure to replace it with something only 25% bugger?
3. Why do you need to build something well over 200 sqm? A couple can live very comfortably in a house with 130 to 160 sqm of internal floor apace.
4. What grounds to you have for thinking that you can beat the market on sqm build costs by sourcing from China? If it was such a good idea the industry would be doing this already. I doubt more than 25% of the material inputs to a house structure could be sourced at a sensible price from 10,000 miles away by sea.
5. The existing property is presumably structurally stable which contrasts with your view that knockdown and replacement with a raft foundation is the route forward.
6. Without building trade skills and 1000's of hours of hands-on labour you will be unlikely to better £1500 sqm build costs during a period of runaway material price inflation and labour shortages.
7. Do you have the cash to fund the £300k build plus another lump sum to demolish and cart away the debris?

In your position I would visit another architect with proven skills in property renovation or extension and see what could be evolved from the existing structure. Replacing the roof could gain you 8 tons which would then allow some lightweight small upper floor to be introduced to provide 45 sqm of upstairs floor area. Insulated plasterboard would boost the wall u-value. Wood cladding or other exterior finish could rejuvenate the street appeal of the existing structure.

 

 

 

[saveasteading]

Back to basics, and apologies if it is already explained. Are you intending to demolish the whole building and simply retain the footings and floor?

If so are you constrained by the existing geometry?

[Zak S]

32 minutes ago, epsilonGreedy said:

@Zak SYou need to go back to the beginning and ask some fundamental questions.

1. When you purchased your plot with a large 180 sqm bungalow, what proportion of the plot value was for the building? Is it habitable? For example if the property cost £350k then it is likely the market value was assessed as £200k for the plot plus £150k for the building in need of £50k of upgrades.
2. Why do you want to spend serious money demolishing this large structure to replace it with something only 25% bugger?
3. Why do you need to build something well over 200 sqm? A couple can live very comfortably in a house with 130 to 160 sqm of internal floor apace.
4. What grounds to you have for thinking that you can beat the market on sqm build costs by sourcing from China? If it was such a good idea the industry would be doing this already. I doubt more than 25% of the material inputs to a house structure could be sourced at a sensible price from 10,000 miles away by sea.
5. The existing property is presumably structurally stable which contrasts with your view that knockdown and replacement with a raft foundation is the route forward.
6. Without building trade skills and 1000's of hours of hands-on labour you will be unlikely to better £1500 sqm build costs during a period of runaway material price inflation and labour shortages.
7. Do you have the cash to fund the £300k build plus another lump sum to demolish and cart away the debris?

In your position I would visit another architect with proven skills in property renovation or extension and see what could be evolved from the existing structure. Replacing the roof could gain you 8 tons which would then allow some lightweight small upper floor to be introduced to provide 45 sqm of upstairs floor area. Insulated plasterboard would boost the wall u-value. Wood cladding or other exterior finish could rejuvenate the street appeal of the existing structure.

 

 

 

Thanks @epsilonGreedy the cost of the purchase is 85-90% in the value of the land. I think there is decent profit in the rebuild of modern well insulated house. Though it's for us to live in we want to spend our money wisely and get most for each pound we spend (like everyone else).

 

My understanding is that fit out actually costs more than the shell and that where we want to save money. The issue with sourcing from china is that you need to have a reliable supply chain contact which I think we have or can pull it off. Around 75% if not more goods used in construction fit outs are sourced from China anyways but we as a customer have to pay profit margins for the retailers. But my plan is to source all in one or two containers. I have to spend a month or so in China so it's not straightforward but I want to see  at least find out the cost differential.

 

We have an Architect. All architects / estate agent advised us of building new house due to value add potential. A new build few houses down the road was recently valued more than three times the cost we paid for this house. Builders think it would cost the same to rebuild as what we have paid for it. Current Sqm is c190 but it can easily be increased to 450-500sqm So by making sure we make the right decision we want to create an asset with maximum value.

Edited December 16, 2021 by Zak S

[Zak S]

13 minutes ago, saveasteading said:

Back to basics, and apologies if it is already explained. Are you intending to demolish the whole building and simply retain the footings and floor?

If so are you constrained by the existing geometry?

Hi yes we would be replacing at least two (side and rear) walls if not three (may be front aswell). I dont think there are any constraints in the existing geometry.

[epsilonGreedy]

21 hours ago, SteamyTea said:

I am happy to cost things out, I charge a very reasonable rate.

 

 

No need, I did the calcs. The u-value difference between 200mm and 300mm of XPS insulation is 0.04 W/m2K.

 

Assuming £0.09 per kwh of heat input, then dropping to 200mm of insulation adds £30 to the annual heating bill or possibly less because in the shoulder months the UFH slab emits less kWs into the house and hence the slab temp is lower.

[epsilonGreedy]

33 minutes ago, Zak S said:

Thanks @epsilonGreedy the cost of the purchases is 85-90% in the value if land.

 

 

That is good.

 

33 minutes ago, Zak S said:

I think there is decent profit in the rebuild of modern well insulated house.

 

 

Always makes ense to cross check that the open market will value the final result at no less than your total project spend. This is just a sanity check even when building a forever house.

 

33 minutes ago, Zak S said:

My understanding is that fit out actually costs more than the shelf and that where we want to save money.

 

 

At a very rough guess I think the split is 50% to water tight shell and across the whole project materials/labour is another 50/50 split.

 

33 minutes ago, Zak S said:

Around 75% id not more goods used in construction fit outs are sourced from China anyways but we as a customer have to pay profit margins for the retailers. But my plan is to source all in one or two containers. I have to spend a month or so in China so it's not straightforward but I want to see  at least find out the cost differential.

 

 

You need flesh out this concept and create your China shopping list. List the items here and see what people think.

 

33 minutes ago, Zak S said:

Current Sqm is c190 but it can easily be increased to 450-500sqm So by making sure we make the right decision we want to create an asset.

 

 

85% of Britons live in a property with under 180 sqm of internal floor space. 450 sqm is a ginormous multi millionaires mansion.

Edited December 16, 2021 by epsilonGreedy

[Zak S]

2 minutes ago, epsilonGreedy said:

 

That is good.

 

 

Always makes ense to cross check that the open market will value the final result at no less than your total project spend. This is just a sanity check even when building a forever house.

 

 

At a very rough guess I think the split is 50% to water tight shell and across the whole project materials/labour is another 50/50 split.

 

 

I think you need flesh out this concept and create your China shopping list. List the items here and see what people think.

 

 

I think 85% of Britons live in a property with under 180 sqm of internal floor space. 450 sqm is a ginormous multi millionaires mansion.

Thanks @epsilonGreedy. China shopping list is a great idea. Will post it here once get to that stage.

 

Point about 450sqm is understood. I think we want to maximise the value as dont want to pass it developer for them to realise all the value.

 

I think reliance on the china calls for a QS to be involved once we have plans so we can see if we are on track. Somebody mentioned the online estimates website. Not sure if anyone has had any experience with them? Given they charge 135.00 I might use them in at the outset based on the rough sketches. I will get my topo/measured building survey and GI report early in the new year (all site work done already).

[SteamyTea]

Worth remembering that epsilongreedy is highly qualified in economics, thermodynamics, the social sciences and property development.

And probably in import and export paperwork.

[epsilonGreedy]

31 minutes ago, SteamyTea said:

Worth remembering that epsilongreedy is highly qualified in economics, thermodynamics, the social sciences and property development.

And probably in import and export paperwork.

 

 

In this thread your expertise is now hidden behind a paywall.

[epsilonGreedy]

56 minutes ago, Zak S said:

I think reliance on the china calls for a QS to be involved once we have plans so we can see if we are on track. Somebody mentioned the online estimates website. Not sure if anyone has had any experience with them? Given they charge 135.00 I might use them in at the outset based on the rough sketches.

 

 

Given your stage of planning the book titled The House Builders Bible will give you a good breakdown of total costs. In the latest edition the author includes alternative building methods since many self builders adopt new building techniques.

Edited December 16, 2021 by epsilonGreedy