Two storey side and rear extension with thermal upgrades

[TomG]

Hi everyone

 

New to the forum, and wanted to chat about some questions we have on our extension. We are getting different opinions from different professionals and it's quite confusing.

The background is, we have bought a 3-bedroom detached house on a lovely street in Nottingham. Its circa 1930's with 9inch brick solid wall constructon. Many of the houses on the street have been substantially extended, but ours is yet to have any work done. 

My partner's Dad is planning to do a lot of the work as he is a carpenter by trade and has spent his life building timber frame buildings and renovating houses. We have planning permission, and we were planning to start this month, but discussions around the internal layout and its affect structurally have caused concerns to be raised by the architect. 

 

The existing plans are below. followed by the proposed plans. The initial proposed plan shows the new kitchen on the left as you look at the house and was the architects suggested layout. However we were'nt happy with the relationship to the living space, and the size of the kitchen considering the extension, we asked to explore removing one of the external stores and moving the utility to allow space for a bigger L shaped kitchen that has some separation from the living space. Obviously this is more complex structurally as long goal-post steel has to go in to support the entire back span of the existing house, wheras previosuly the the utility room wall was load bearing. 

 

The architect has also raised concerns about using timber frame as the foundations for the new extension would be bigger, and another goalpost required over the rear bifold/sliding doors. Whereas with loadbearing masonry apparently a steel goalpost would not be required and the foundations smaller. 

 

We are now struggling to decide between the layouts. My partner's father has got a second structural engineers opinion (a structural engineer he knows and works with regularly) and both believe the revised layout is workable, but the architect is strongly against. Any advice would be warmly received. To timber frame or not? To Kitchen flip or not?

 

Existing Plan....

• Initial proposed Plan

 

• Revised internal Layout

 

 

Edited May 9, 2021 by TomG
typo's

[TomG]

This is our property, and also the propertt two doors down to give an idea what others have done. We are not planning to go all the way to the neighbours as they have, as we want to keep an access down the side of the property.

 

 

[saveasteading]

I have not studied this in detail, but do note that the bifold door opening is a very large proportion of the wall. There will be a structural steel here whatever. The extra cost of adding posts and enlarging the footings is not huge.

Your decision may be based on other factors.....availability of skills and materials, and how the rest of the structure works.

Explain to Engineer and Architect what you want/are considering, and why, then allow them to make it work for you.

[TomG]

Thanks for your reply.. That's what I figured. There will be a steel across that rear opening regardless, whether that steel sits on steel goalposts or loadbearing masonry, I assume the load transferred to the footings is still similar and so the sizes should be similar. The issue the architect is raising is more the relationship to the neighbours garage, and that the pads the structural engineer has desingned would undermine the garage footings. Their isn't anything we're too worried about with the rear opening, as if need be I'm happy to compromise on the size of that opening. Say going from the current 5.5m opening to a 4.5m opening. It's North facing anyway, but I'd liked the idea of a kitchen and living space that worked well with a garden patio in the summer. 

 

The bigger concern is the structure around the existing rear elevation. The pads the structural engineer designed initially encroached on to the neighbours drive (so a no go), and we subsequently tweaked them, however there were still concerns that the design would undermine the foundations to the neighbour on the right of the property. Interestingly the structural engineer has designed the footings assuming clay, however next door have told us their soil was sand, and a hole I've dug in the garden along the proposed rear elevation suggests the same. The pads and opening across the entire existing housee do make a complex build, but we're wondering if they are significiantly over engineered, especially with the ground conditions? I've shown the footing design below.... might be more appopriate for me to post in the structural forum.

 

 

 

[MikeSharp01]

That is a massive pad! So there must be some serious load there and I am reminded of the bible story about the chap that built his house on sand. Talk to the SE about a capped screw pile pad. That might be possible in a tighter space for the same load bearing capacity. 

[TomG]

4 hours ago, MikeSharp01 said:

That is a massive pad! So there must be some serious load there and I am reminded of the bible story about the chap that built his house on sand. Talk to the SE about a capped screw pile pad. That might be possible in a tighter space for the same load bearing capacity. 

 

 It is indeed, that's what everyone who has seen the plans has said. Admittedly there is a large steel across the entire rear wall of the house so I guess we should have excepted it to be substantial. Although I do wonder if things like the direction of the span of the floor joists in the upstairs bedroom affect loading, and these have never been checked with a site visit at any point. 

 

Indeed. Unfortunately we didn't build our house on sand as in the bible....we me acquired an already build house on sand...oops. Although I hear that sand can be preferable to clay. Moving the house to better ground conditions seems excessive just to get the kitchen we want ?

Edited May 9, 2021 by TomG

[MikeSharp01]

Havent done the math although I think the load might actually be quite low but the pad is on sand so is thick to allow it to spread the point load hence the reinforcements and the area is big because of the bearing capacity of the sand being quite low.

 

Its a scenario your SE can explain but if it is all about area there might be other ways of achieving it. IE make it deeper with more reinforcement and longer and thinner. (More like a beam than a pad.)

 

The low load, if this is the explaination - others are possible, also helps with the beam across the space. 

[saveasteading]

Looks right to me, as you are taking out an awful lot of wall, and putting the load on this one point.

Sand/Clay doesn't isn't relevant and SE will have allowed accordingly.

The ambitious knocking out of walls makes the solution difficult and has costs.

 

You might want to avoid going deeper as you get into party wall issues. However, if neighbour is friendly and reasonable they might agree that it doesn't have to get formal. Talk to SE about that.

You can't make the pad too asymmetrical either.

Poss to link the 2 pads inside the house so that you can bring in the outer edge. ie a continuous beam with a lot of reinforcement? as above. Ask.

 

Also note that the outside found'n clashes with a drain pipe.

The pipe is making the outer edge of the pad pretty useless.. Another reason to bring inwards.

If it remains in conflict with the found'n, then the pipe needs to be wrapped with polystyrene before pouring , so that it is independent and doesn't break.

[TomG]

Thanks both. Helps to get a bit of a sense check, and assumed it was due to the full removal of that back wall.

 

I'll explore the possibility of linking the two pads as suggested to see if this will help brink it in further from both neighbours.