First floor extension design

[oldkettle]

Hi,

 

I have had a visit from a BCO who confirmed the foundation of our bungalow seems fine to take the load of an extra floor. Not sure whether I need to get it confirmed in writing but it is something for now. So I started looking at our plans more carefully.

 

The option that we have so far is primitive : the first floor will have the same footprint as the ground floor with the exception of the bay window - see primitive sketch one for the view from the back, which is almost exactly east side. But that means we will be blocking already limited light for the large room on the right, like it is currently blocked for the living room on the ground floor.

 

So what if we go for cantilevered option - it only need to go out by about 1m. It seems to make certain bits much simpler but probably requires a steel support. Would it be substantially more expensive to build? Any advice please?

 

Joseph

 

[ProDave]

I would seriously look at extending the ground floor by that 1 metre so it enlarges the living room and solves the shading issue of the living room window and obviously solves the issue for upstairs as well.

 

Yes it's a new strip of foundations for that bit but probably no harder or more expensive than trying to cantilever the upstairs (which would only solve the shading issue for upstairs anyway)

 

I sometimes despair why the original designer stepped it back like that without regard to the shaddow it would cast. 
 

[oldkettle]

39 minutes ago, ProDave said:

I sometimes despair why the original designer stepped it back like that without regard to the shaddow it would cast. 
 

That's what I said! There is about 50m of the garden, why not make this side longer rather than shorter is beyond me.

 

What extra cost (very roughly) are we talking about here if I were to extend downstairs? Digging foundation very close to the existing one, building 5m of the new wall probably with ICF? Will we be able to reuse the window and the door or will we have to buy new ones? 

[AliG]

It's going to cost no more to extend the downstairs floor than build a cantilevered upper floor. Hard to say exactly, a few thousand pounds. The cantilever will have to hold up the whole wall and roof weight above. Often the cost of extending out the ground floor is steel support for the upper floor. In this case you are avoiding that. You are also fixing a problem that you have with shading. If anything you might want to extend that area to stick out past the rest of the house and then put in a  window that faces south.

 

If they are in good condition there is no reason that you can't reuse the door and window, although it will require taking them out carefully!

 

Why would you want to build in ICF for such a small area? It will likely be more expensive than traditional methods and you won't gain any benefit from insulation or air tightness and it will only be a tiny percentage of the house.

 

 

[oldkettle]

12 minutes ago, AliG said:

It's going to cost no more to extend the downstairs floor than build a cantilevered upper floor. Hard to say exactly, a few thousand pounds. The cantilever will have to hold up the whole wall and roof weight above. Often the cost of extending out the ground floor is steel support for the upper floor. In this case you are avoiding that. You are also fixing a problem that you have with shading. If anything you might want to extend that area to stick out past the rest of the house and then put in a  window that faces south.

 

If they are in good condition there is no reason that you can't reuse the door and window, although it will require taking them out carefully!

 

Why would you want to build in ICF for such a small area? It will likely be more expensive than traditional methods and you won't gain any benefit from insulation or air tightness and it will only be a tiny percentage of the house.

 

 

I did think about extending this side more because it would cost almost the same and there is plenty of space. The only small downside is since we are on a slope from the garden towards the road some landscaping would be required. As long as the cost is manageable we will definitely consider it.

 

You are right, it is only a small percentage, the main reason to use ICF would be speed - my naive understanding is it is much faster to build. Well, probably also not having to worry about finding a very good brickie and not having to think about insulation. On the other hand, I was planning to add external wall insulation downstairs when money is there, not sure how it would work with part ICF part cavity wall.

 

Is it substantially more expensive to use ICF for such a short wall?

 

 

[AliG]

I think it is highly unlikely you will be able to find a builder who knows how to work with ICF who is interested in such a small job and very few builders know ICF at all. It will be a lot easier to find a brickie.

 

It won't take long to build such a small area however it is built.

 

Assuming that the bungalow is brick/block built with a cavity wall, I would be tempted to build out the ground floor in the same way then have a timber frame built that sits on top of it for the upper floor. That would probably have the least issues with the weight you are putting on the downstairs walls and foundations.

 

I believe there are a lot of issues with adding EWI to a house that wasn't designed for it. I think people might recommend adding polystyrene bead insulation to the cavity which if it works would be a much easier and probably cheaper job as you won't need to recover the outside walls. But there are a lot of issues with this kind of job in terms of damp and it might be an idea to try and figure it out, even if you don't actually do it, before you extend upstairs.

 

[oldkettle]

Yeah, I keep forgetting there are jobs that are too small :-( It just feels such a shame to build using inherently bad method then try to resolve issues with it.

13 minutes ago, AliG said:

IAssuming that the bungalow is brick/block built with a cavity wall, I would be tempted to build out the ground floor in the same way then have a timber frame built that sits on top of it for the upper floor. That would probably have the least issues with the weight you are putting on the downstairs walls and foundations.

 

I believe there are a lot of issues with adding EWI to a house that wasn't designed for it. I think people might recommend adding polystyrene bead insulation to the cavity which if it works would be a much easier and probably cheaper job as you won't need to recover the outside walls. But there are a lot of issues with this kind of job in terms of damp and it might be an idea to try and figure it out, even if you don't actually do it, before you extend upstairs.

 

It is brick and block and unfortunately there is fibre insulation from 1995 which is apparently quite expensive to get rid of. There are no problems with damp that I am aware of. Since we are on a slope only on the garden side the floor is one step above the ground level, at the front there is almost a meter of the wall below DPC, may be it helps with drying out. Is it internal moisture that I should be concerned about? It is a real pain finding reliable information on insulating cavity walls properly.

 

We are only considering TF first floor at the moment. There is still an unresolved issue with positioning of the frame. I am trying to get a 300mm twin wall but then it will have to rest on both internal and external leaves which I guess is a problem if the external leaf is cold - this is one of the reasons I wanted EWI.

 

[mikalscad]

if the bco has said it's OK then i'd submit drawings to the council then you'll have official approval