Buildability of first extension

[Rednblack]

Hi, newbie here, about to (hopefully) embark on my first extension.

The extension is a narrow 2 storey extension to the side of the house. It will involve removing a large portion of the existing gable wall at both ground and first floor level.

My concerns are about the buildability of the works involved in knocking through, bearing in mind we will be living in the house during the works. I thought I'd try and get a general consensus here before wasting the time if any builders.

First concern is when the knock through may need to be done. Ideally I'd like the side extension built and made waterproof and insulated prior to taking down the walls, but I am concerned if this will be possible when looking at the installation of the steels and also new staircase?

As a complication, the cavity walls were filled with beaded insulation 20 odd years ago and I am concerned how much I will lose when knocking through? I imagine I will lose all of the insulation to the gable wall and a fair bit from the front and rear elevations. What long term implications will this have on my house? Will I need to get it professionally removed before the start of the build and reinstated at completion? Presumably next door will have also been done...how will this affect their house?

I do have some background in the building industry, but from behind a desk and not from a point of view if the practibility if on site work!

Thanks in advance of your advice/comments.

210409 - STRUCTURAL DRAWINGS -S2.pdf 210409 - STRUCTURAL DRAWINGS -S1.pdf

[Rednblack]

210409_-_BUILDING_REGS_DRAWINGS_-BR1.pdf

190416 - PLANNING DRAWING -01(3).pdf

Edited April 17, 2021 by Rednblack

[tonyshouse]

I would take down a 4 to 600 wide pillar of the g/f flank wall at least before building the g/f new walls so things can be tied in nicely.

 

I don’t like the butt join at the bottom of the stairs, this will crack 

 

upstairs needs thought lots of cold bridging going on with the old and new gable walls 

[Rednblack]

Thanks for your reply.

Where do you mean when saying take down 400-600mm of wall? Do you mean the rear kitchen wall and by the porch?

The butt joint...do you mean where the post is in the inner skin of cavity wall? We will shot fire SS ties to the post and if we put chicken wire mesh behind/in the plaster it should be ok, shouldn't it?

Thanks for the comment about cold bridging, I will look into that. Where is the cold bridge you would be worried about?

Edited April 17, 2021 by Rednblack

[tonyshouse]

Take down the outside skin from 105mm back from the back corner to 525mm back and a similar slot at the front so that you can see the interna skin at the corner.

 

beads should be glued together but will need protection 

[Rednblack]

2 hours ago, tonyshouse said:

Take down the outside skin from 105mm back from the back corner to 525mm back and a similar slot at the front so that you can see the interna skin at the corner.

 

beads should be glued together but will need protection 

Thanks. However, I'm not sure they are glued...I had a problem with damp just after I moved in about 16 years ago...we opened up a small hole and from memory they were pretty loose?

Also, what about the butt joint and cold bridging you mentioned? 

Where are you worried about a cold bridge? I've looked at the plans and cannot see an issue?

[tonyshouse]

But join at bottom of stairs,  cold bridging up into gable wall 

[Rednblack]

38 minutes ago, tonyshouse said:

But join at bottom of stairs,  cold bridging up into gable wall 

Can you please expand on that? 

I assume you mean where the steel is in the wall, but, as I said above, SS wall ties will be shot fire fixed to the steel and mesh in the plaster.

I cannot see a cold bridge...the existing cavity is insulated (assuming we don't lose the beads) and the new rafters will be insulated too. Where is the cold bridge?

[Mr Punter]

Quite complicated for the 20m2 of space you are gaining.  You need a very competent builder for this.  Is there no way you could move out for a while?

 

I would leave it to the builder to decide on the wall insulation.  It may be best removed then reinstalled.  Get it surveyed first.

 

I would be interested to know what prices you get back.

[PeterW]

Can’t see the benefit of that build tbh as it’s going to cost you probably £50k and you have very little extra space. 
 

I would also be checking which way joists run - there could be some real complications. 
 

You could do some value engineering on that which would mean you could leave a lot of the walls intact. For example, that widened hallway is pointless - just put a door into the WC. 

Also the bathroom door swings the wrong way - a standard 762mm door will cover most of the room - you won’t be able to easily walk round it. 
 

Is there any reason you want to extend rather than just move as I doubt you will get your money back on this. 

 

[Rednblack]

3 hours ago, Mr Punter said:

Quite complicated for the 20m2 of space you are gaining.  You need a very competent builder for this.  Is there no way you could move out for a while?

 

I would leave it to the builder to decide on the wall insulation.  It may be best removed then reinstalled.  Get it surveyed first.

 

I would be interested to know what prices you get back.

Thank you for your reply.

I was thinking the family could visit relatives abroad, as long as we time it right to coincide with the school holidays, when we knock through the walls.

I also think it is complicated, hence my post title. Hopefully it is acheivable though.

Price wise, I'm expecting circa £60k, as the next post suggests.

[Rednblack]

1 hour ago, PeterW said:

Can’t see the benefit of that build tbh as it’s going to cost you probably £50k and you have very little extra space. 
 

I would also be checking which way joists run - there could be some real complications. 
 

You could do some value engineering on that which would mean you could leave a lot of the walls intact. For example, that widened hallway is pointless - just put a door into the WC. 

Also the bathroom door swings the wrong way - a standard 762mm door will cover most of the room - you won’t be able to easily walk round it. 
 

Is there any reason you want to extend rather than just move as I doubt you will get your money back on this. 

 

Thank you for your reply.

The joists run front to back, so no problem there.

I have looked at leaving the wall but it would mean a long dark corridor leading to the WC.

I acknowledge your comment about the bathroom door.

With regards to extending rather than moving, the house is in a really good location with direct access to a park at the back and excellent schools nearby. The 4th bedroom is necessary for relatives visiting from abroad and the 2nd WC is essential with a family growing up.

The house, as it is, is worth maybe £310k. A similar 4 bed home (detached - there aren't many semi detatched) in the area will be £400-425k. A £50-60k extension is definitely the cheaper option, even if I won't get it back if I needed to sell immediately (which I won't)