How to extend a poured concrete house

Mollyobs

I have searched and read every thread that seemed vaguely relevant, but I'm at a loss.

We are planning to renovate and extend a house which was built of solid concrete in the 30s. This would involve demolishing several old flat roof bits and adding a two-storey extension coming to about 800 sq ft.

There is no insulation currently installed anywhere.

Options suggested by various 'experts' (builder, arch tech, BER guy) so far are:

1. Dryline old house, standard cavity + dryline extension.

2. Dryline old house, hi-spec timberframe extension.

3. Block on flat extension, External insulation around everything.

4. Knock the lot and start again... :rolleyes:


With 1 & 2 will we end up with moisture gathering behind the insulation in the old house? and lose loads of room to 10cm of insulation?
Will one side of the house suck the heat from the other?
What about thermal bridging where the two construction types meet?
Will EWI blow away in the wind or get eaten by birds (as per other threads!)

What would you do?

Poor Uncle Tom

Every house is different. Some of those shuttered concrete houses were built with sea sand and gravel others were built with washed agrigates. I have knocked some due to damp and others were bone dry. Some have poured bitumen DPC's and sprung timber floors, if this is the case and your house is dry it might make a candidate for extension, if not it might not be economical to keep it.

Remember what you don't have in a 1930's cottage:
Radon sump or barrier,
DPM's
Floor insulation,
Wall cavities,
Wall insulations,
Roof insulations,
Modern room sizes,
Possibly poor electrics,
Possibly poor plumbing,
etc.,

Mollyobs

Thanks for the quick reply Uncle Tom.

It's a decent house with 4 good-sized rooms, suspended timber floors, picture rails, nice bays... the engineer who surveyed it said it was in good condition, and the original section is bone dry.

We'll probably be taking up the ground floor to install insulation and UFH, so the Radon barrier will be put in at that stage.

So assuming I can proceed without 'knocking the lot'...

Any suggestions on the pro's and con's of the possible extension methods?

Mellor

Mollyobs wrote: »

Options suggested by various 'experts' (builder, arch tech, BER guy) so far are:

Are you sarcasticly suggesting that these guys are less than experts (may well be) or just highlighting the words. it's hard to pick up your tone. If there are issues with the professional then I'd sovle them before proceeding on a job liek this.

1. Dryline old house, standard cavity + dryline extension.

2. Dryline old house, hi-spec timberframe extension.

Not a big fan of either of these. If you plan to upgrade the original do it right.
Where they meet will be messy. I'd prob prefer if the extensino was thermally separate to these options.

3. Block on flat extension, External insulation around everything.

4. Knock the lot and start again... :rolleyes:

I like both of these options.
Assuming EWI is suitable, I can't see what the issue is. Blow away in the wind???

I'm also not sure what you inserted :rolleyes: after option 4. Knocking it could easily be the best option. But nobody can answer that over a forum.

rayjdav

Poor Uncle Tom wrote: »

Every house is different. Some of those shuttered concrete houses were built with sea sand and gravel others were built with washed agrigates. I have knocked some due to damp and others were bone dry. Some have poured bitumen DPC's and sprung timber floors, if this is the case and your house is dry it might make a candidate for extension, if not it might not be economical to keep it.

Remember what you don't have in a 1930's cottage:
Radon sump or barrier,
DPM's
Floor insulation,
Wall cavities,
Wall insulations,
Roof insulations,
Modern room sizes,
Possibly poor electrics,
Possibly poor plumbing,
etc.,

OP,
Basically EVERYTHING PUT has said here is 100% true. Did our own house recently enough, 1930's cottage. In hindsight, would have been far better with all issues that arose to have actually knocked it and start from scratch.

From a workability/living point of view, I had to rearrange the whole internal (i.e. knock/build walls/opes etc.) of the existing to allow for modern comfort, instead of making do. Ours was built with homemade blocks and sea sand. Bloody knightmare when it was stripped:mad: Stripped to allow for new internal conc floors up. Only way. Also, the structure of the house was dodgy to say the least so extreme care had to be taken when doing certain works.

So this is why I would advise, naturally if the budget/time/planning allows, knock and start from scratch. Basically your No.2 option is what we did, dry-line and TF extension to side. Imho you'd only be making do if you did anything else;)

If you plan doing any works to the structure, walls/roof, seriously, get an Engineer to have a look first to see if it is feasable/economical, (it's always possible:D)

Mollyobs

Mellor wrote: »

Are you sarcasticly suggesting that these guys are less than experts (may well be) or just highlighting the words. it's hard to pick up your tone. If there are issues with the professional then I'd sovle them before proceeding on a job liek this.

Sorry, tone is a tough one. I was trying to highlight the fact that I'd already consulted all those professions/trades to emphasise that this wasn't a 'spur of the moment' question. It's been going on for a few months now, and it's wrecking our heads!

I suppose if any two of the people we consulted had come up with the same answer, we'd be more inclined to go with that as the best option.

The 'knock it' suggestion had come from a design point of view rather than a structural one. The engineer was very positive about the old part of the house. The rolleyes were because it would be my least favoured solution.

Mellor wrote: »

Assuming EWI is suitable, I can't see what the issue is. Blow away in the wind???

One poster on the EWI threads is always raising wind-load as a factor. I don't know enough to understand if this is a major concern.

Mellor, Thanks for making a call on 3 & 4 being the better options. It's hard to make the choice when you are learning this as you go along, and getting conflicting advice.

rayjdav, thanks for the info. Do you find any issues keeping old and new sides of the house at the same temperature?

sydthebeat

Mollyobs wrote: »

One poster on the EWI threads is always raising wind-load as a factor. I don't know enough to understand if this is a major concern.

.. some posters can be evangelical in their conspiracy theories..... :rolleyes:

BryanF

sydthebeat wrote: »

.. some posters can be evangelical in their conspiracy theories..... :rolleyes:

it's better than 'I told you so'.. & worth the debate I think you'd agree ..

rayjdav

Mollyobs wrote: »

rayjdav, thanks for the info. Do you find any issues keeping old and new sides of the house at the same temperature?

If you mean from a heating point of view, no. House is set in 2 zones, bedrooms (old part) and living (TF ext). Simple to heat. Add to that all beds are east so have natural morning light and other areas south & west so sun, when there, the whole day as required per area.

I also went to town in the old part in the installation of insulation, from new UF, 4" wall slabs and +300mm to attic. If I could have done more I would have to floor /walls but had knock on effect. Been one bad winter in and no complaints from "The Boss":rolleyes:

Having said all that though, if it was again, and knowing what I do now about the original structure, I would have floored it in an instant and built from scratch.:D So, if it is similar to mine, imho go for your Option 4.

aghbren

been down that road also and after stripping house to 4 external walls (as the more you expose the more problems you find, along with the difficulty of modifying the existing ops) we decided to flatten and start again and once that decision was made have never looked back

Mellor

I think knockign it appears to sound worse than it is.
if the house was in very good shape, where it wasn't justified to knockl it I would either;

A) External insulate it along withthe new section
or
Construct the extension as a separate stucture, fully insulated on all side (i'd also reduce the areas of contact to achieve this. Have this as the modern warm section, and get the old house to as good as possible.

Mollyobs

Thanks for all opinions.

We're talking to in the engineer again to make sure the old house is extension worthy. And leaning towards the EWI block on flat extension.