Single story side extension planning - thoughts on layout and costs??

Lunielumps

Hello!

I'm working on some preliminary single-story side extension plans - we have a 3m wide drive running run the side of our semi detached house. 
our neighbour on the other side of the driveway (seperated by a fence) has a 80cm alley and then their own single story side extension. 

We want to use our extension to create an open plan kitchen & downstairs toilet, and we are planning on moving the boiler, electricity fuse box & meter out of the hall and into the extension. 

Existing floor plan: https://ibb.co/0jKcMV6

Extension idea: https://ibb.co/2vR5S4Y

We also really want to maximise the 3m width as much as possible - but not sure minimum space we need to leave for guttering and footings etc beside the bourndary (fence is ours). 

What i have drawn would add just shy of 20m2 to the ground floor. 

Any thoughts welcome!

Section62

You'd be removing part of the corner of the house - this is typically an expensive way of adding m2 to a house, especially if the wall being removed is part of a gable wall (is it, or is the roof hipped?)

It also appears you'd be removing a chimney breast - is there an existing stack all the way up to the roof?

You'd lose access to the rear of the property - what do you use the garden for, and would you be Ok taking stuff through the house to get to the garden.

A rear extension may give you more for your money, subject to how large the garden is and other factors such as level differences.

Lunielumps

Section62 said:

You'd be removing part of the corner of the house - this is typically an expensive way of adding m2 to a house, especially if the wall being removed is part of a gable wall (is it, or is the roof hipped?)

Thanks for your reply

Sadly a rear extension isnt an option due to garden size, which also means we arent concerned about loosing external access. 
The chimney stack is already removed so the chimney breast on the ground floor isn't an issue.

Yes that wall is a gable wall - what is it about opening up this stretch that would be especially challenging?

Section62

Lunielumps said:

Yes that wall is a gable wall - what is it about opening up this stretch that would be especially challenging?

Gable walls are extra tall, so more weight to be supported by a beam if you open the wall up.  The corners of traditionally-built houses are what gives the structure most of its stability.  Removing a corner usually means the need to provide some alternate means of lateral support to at least one wall.

Slinky

Haven't looked at your plans, but our new extension walls are 34cm thick and the overhanging gutters are about 30cm.  So that's 64cm lost before you start

Lunielumps

Slinky said:

our new extension walls are 34cm thick and the overhanging gutters are about 30cm

Out of interest when was yours built? I had conservatively been estimated 40cm thick walls, so if they were 34cm i'd consider that a win!

Doozergirl

Slinky said:

Haven't looked at your plans, but our new extension walls are 34cm thick and the overhanging gutters are about 30cm.  So that's 64cm lost before you start

An extension can be designed so that it's a gable or a flat roof and doesn't need guttering, or with a concealed guttering detail on the inside side of the wall rather than outside.  

If people considered building with a modern construction method, the walls could be less than 300mm thick.   My OH also had a brick wall through on the new regs at 300mm by using solely solid insulation in the cavity.  

Slinky

Last year.

casper_gutman

We did something fairly similar to this. The initial sketch I did looked very similar to yours, but in the end we decided to keep a side access like your neighbour. If the garden was smaller we'd probably have chosen to maximise the width as you have shown.

As others have said, removing the corner of the house will make things tricker from a structural engineering POV. If you can leave a section of wall there might make things easier, otherwise budget more than you think for steelwork!

I recommend chatting with a structural engineer early, before spending too much money on drawing up plans, in case there's an easy tweak you can make that will save the budget.

Cost is obviously very dependent on finishes you go for, but we spent about £100,000 on the entire project, which was finished in 2021. This included demolishing the garage and fitting out the new kitchen, utility and loo including flooring, tiles. Landscaping outside was on top of that.