Bungalow to house conversion - advice - switch to rebuild?

[PhilC]

Hi Everyone,

 

I'd appreciate any advice or guidance you can share. I've been putting together a project to convert our detached chalet bungalow into a house. We have householder development planning granted and I have a 3d structural design/SE calcs done (not a building control application completed, was looking to go via build notice) and quotations from timber frame suppliers and builders.

 

The new first floor would be timber frame (or SIPS). It's been very hard to get builders engaged, I guess a state of the market generally but also I think because of the complexity of the build around matching the ground floor masonry to the timber frame 1st floor and handoffs between different people. The full costs of the quotes were way above our expectations and are not now realistic to our budget. We have spoken to the timber frame suppliers and received quotes for a full build for our design and it's only a small increase in the previous extension quote. When I factor in other aspects around the timber frame structure with industry per m2 rates for foundation, veneer wall, render, windows, roof etc, the build cost and VAT reclaim makes this look significantly cheaper and enables us to avoid complex retrofits of the ground floor to achieve the insulation/airtightness we are looking to get, so the new build seems a more viable route and probably a better outcome.

 

I did do some reading on new build early in the project but dismissed it as too complicated and thought it would be cheaper to re-use the ground floor.

 

Appreciate if any of you can share your advice on what I should be thinking about here I have a few areas I am researching but I am pretty sure I am missing important things I should consider.

 

Thanks in advance for your time to respond.

 

[Bonner]

Most people will say rebuild because of the complexity and risks involved with extending. Also you will undoubtedly end up with a better home. However you should get a full costing done, don’t rely on m2 rates to make a decision.

[Iceverge]

The quotes from the builders are more than lightly high to get you to clear off. 

 

Nobody wants the hassle of an awkward extension Vs a new build. 

 

Do you have any plans to share? Without seeing them I'm going to guess that you'll be better off starting with a clean sheet design for a knock and rebuild. 

[Nickfromwales]

17 hours ago, PhilC said:

I am pretty sure I am missing important things I should consider.

One cheat is to build new, over existing foundations. If you can live with the current layout then a TF or ICF build atop would be a money-saver. Feasibility needs doing by the lorry-load though, so consider your choices. My 2 cents is knock it down as you'll spend the same amount on lipstick for a pig as you'll spend on new (taking into account your zero VAT status with a new build).

Just be mindful that a new build with new foundations would need to specified for 'made up / disturbed ground' so you'd likely be better off with an insulated raft at that stage, which is a very good option indeed.

Good luck either way, but trying to retro-add airtightness and insulation during a hybrid build is a massive PITA. I'd just stick with masonry at that stage, and observe one discipline throughout, as long as the foundations could take the second lift of masonry.

 

Knock it down  

 

[Conor]

What Nick says. Clear to the footings. Not having to redo services and groundworks will be a huge saving, time and money.

 

 

[PhilC]

On 25/06/2023 at 08:27, Iceverge said:

The quotes from the builders are more than lightly high to get you to clear off. 

 

Nobody wants the hassle of an awkward extension Vs a new build. 

 

Do you have any plans to share? Without seeing them I'm going to guess that you'll be better off starting with a clean sheet design for a knock and rebuild. 

Thanks, will share plans, the planning portal seems down at the moment so cant grab a link

[PhilC]

On 25/06/2023 at 09:37, Nickfromwales said:

One cheat is to build new, over existing foundations. If you can live with the current layout then a TF or ICF build atop would be a money-saver. Feasibility needs doing by the lorry-load though, so consider your choices. My 2 cents is knock it down as you'll spend the same amount on lipstick for a pig as you'll spend on new (taking into account your zero VAT status with a new build).

Just be mindful that a new build with new foundations would need to specified for 'made up / disturbed ground' so you'd likely be better off with an insulated raft at that stage, which is a very good option indeed.

Good luck either way, but trying to retro-add airtightness and insulation during a hybrid build is a massive PITA. I'd just stick with masonry at that stage, and observe one discipline throughout, as long as the foundations could take the second lift of masonry.

 

Knock it down  

 

Thanks Insulated raft was what I was thinking

[Nickfromwales]

Just now, PhilC said:

Thanks Insulated raft was what I was thinking

Will be the best investment you can make. 300mm of EPS and 100-120mm of concrete in the slab, with the UFH pipes stitched in, and away to go. Just be mindful to watch the SE detailing the height of the mesh / chairs so you retain sufficient concrete cover over the tops of the pipes. Prob better to get 40mm chairs max and accept a slump in the steel to around 25-30mm (which is fine for the underside of the slab for protection against atmospheric moisture absorption).

[Iceverge]

2 minutes ago, PhilC said:

Thanks, will share plans, the planning portal seems down at the moment so cant grab a link

 

Cool, however it might be better if you were to remove any personal info first, just in case. 

[PhilC]

On 25/06/2023 at 10:07, Conor said:

What Nick says. Clear to the footings. Not having to redo services and groundworks will be a huge saving, time and money.

 

 

👍 looking at most raft designs I don't see a use for the cavity wall, my footings at around 900mm deep. So, I guess I level off and hardcore between my existing sub-ground cavity wall to the bottom of the raft level? if I am not moving the perimeter of the building.

[PhilC]

Just now, Iceverge said:

 

Cool, however it might be better if you were to remove any personal info first, just in case. 

Will have a look, should be fine planning portal is public anyway.

[Nickfromwales]

2 minutes ago, PhilC said:

👍 looking at most raft designs I don't see a use for the cavity wall, my footings at around 900mm deep. So, I guess I level off and hardcore between my existing sub-ground cavity wall to the bottom of the raft level? if I am not moving the perimeter of the building.

That will be down to the SE to say, tbh. We don't know the ground conditions so cannot comment here definitively.

[PhilC]

5 minutes ago, Nickfromwales said:

That will be down to the SE to say, tbh. We don't know the ground conditions so cannot comment here definitively.

Timber frame people who i have been discussing the project with have a foundations company who they have worked with on their previous builds, will get in contact with them.

[joe90]

My last build was a demolish and new build after years of extensions and refurbs and it was a dream, I was lucky getting a main contractor who was good but loved the journey. Go new build (and get the VAT back).

[saveasteading]

One more thought to add to the good advice. 

Subject to the existing construction.

 

The existing foundations should not be enough to support an additional floor. If they are, then they were overspecified originally, so the SE will assume they are insufficient. Thus you need expensive widening of the footings or some clever redistribution  of loads to new, extra foundations.

IF adding an extra floor, I think Sips is too limiting in precision. I suggest a stick build. It can end up being effectively sips, but it will fit whatever geometry you have.

 

Summary. Diy ....reuse all below ground construction but allow extra footings

Builder?   Knock it down.

 

[Nickfromwales]

1 hour ago, saveasteading said:

I suggest a stick build. It can end up being effectively sips, but it will fit whatever geometry you have.

+1, and would be deliciously simple.

[carljarrett]

Hiya not sure if this is still open or relevant, however I have taken on a bungalow to house renovation myself. I am an engineer by trade never done building work and I am currently battening the outside ready for render boards. I put timber frame in stick form straight on top of the bungalow walls and then trusses on top to give us a 11.2 m long by 4.2 m wide, 2.4 m high room in the loft. It’s more than doable. I’m quite the celeb on my main road now lol. I’ve done it all on my own other than standing the trusses up where I had my fiancées grandad help as they were fooking huge ! 
 

the hardest bit was working out the connection between the old and new, I chemical fixed studding deep into the bungalow brick walls and fixed the timber sole plate down via the studs plus wall restraints etc as per normal standards. I’m self taught from YouTube mainly

 

I would say the tricky bit is the render transition from timber to original bungalow brick, especially as we are insulting externally on the downstairs so I had to build the timber frame above with an adequate overhang so it finishes somewhat flush with the downstairs EWI.

 

my bungalow is a wonky rectangle, so I had to build a nice true new structure on a wonky substructure. Which will need to be made up and hidden within the battening and render board.

 

I basically have 4 steels running across the bungalow which meant I was free to knock all internal walls down if I desired so gave us huge scope to redesign. There as no point starting a new with our build as the size and shape already made best use of the plot. 
 

it’s all going on YouTube too