Neighbouring rear extensions - should we share party wall?

[Chris S]

Hi,

We have recently moved into our new (terraced) house and are about start planning a rear extension. Our next door neighbour's are about to start building work on their similar extension in just 3 weeks time.

 

If possible, it would be mutually beneficial in terms of space that we share a party wall along the party line, rather than each setting a ~300mm thick wall 150mm from the party line. We'd both gain ~300mm on the width of our extensions, which is a lot given that we are both fitting two rooms across the width of the extensions.

 

However, I am aware that we may have just missed the boat here and we don't want to add any unneccessary complications. So before raising the idea I want to be sure it is a good idea. Please can you give me your thoughts.

 

Here are a few points to note:

1. Our neighbours are pretty much ready to go with all the drawings and permissions etc and a start date. This change would have a number of impacts on their design. Would it affect their planning permission too? (which states offset from party line).
2. We don't yet know if we can afford to extend as far out as our neighbours (5m from house).
3. We don't yet know if the height of our extension will be the same as our neighbours.
4. We are extending on the first floor (over the middle of the ground floor extension), so the wall in question will have a universal beam terminating at between 3 and 3.6m from the house. Hence the foundation requirements may be different to that of our neighbour's.
5. There is a sewer running parallel at 3m from the house, making the above point a little trickier. (Our neighbours drawings for bridging the sewer appears to meet Thames Water's requirements.)
6. If a wall is built on the party line and it turns out to be inadequate for our use, presumably we would have to build a new wall futher inside the party line and hence end up loosing space.
7. If a wall is built on the party line, can the remainder of our foundation be satisfactorially joined up with the party wall foundation? And can our rear wall be satisfactorily interleaved with the party wall?
8. There may well be other complications.

 

I may have just talked myself out of it by writing this post, but am interested in your thoughts.

 

The plan is that I will do the majority of the architectural work with the support of various resources. We will employ the services of a structural engineer and use a good builder who can advise us too. I am a design and project engineer of electro-mechanical products for various industries, hence I have a solid engineering approach but don't have much experience in the specifics of the architectural application. So I'm more self design than self build - I hope that is ok on this forum? I'd love to build it myself but its just not practical for us.

 

Attached is a rough drawing of our proposed extension, viewed from the rear. The party wall in question is shown by the red line.

 

Thanks in advance!

 

[Ferdinand]

THank you for a clear post with full information. WOuld you care to do an introduction over on the Introduce Yourself sub-forum ... it is always good to have ?

 

I think this probably depends mainly on how much your neighbours value their extra 300mm vs the potential delay.

 

Your Council will tell you how long it would take depending on what is involved permissions-wise etc, as I assume your neighbours have PP to go that close to the boundary. Perhaps it could go through as a minor change?

 

Technically I see no reason why the two have to be built together, as you could tie into the party wall afterwards (leave bricks sticking out or sockets)? But in that case watertight agreements will be crucial and you need to know you will be supported, and there are a few risks such as if yours does not get PP.

 

Personally I think I would want my PP Application in with a neighbour letter of support before they start building. IF they have to change their PP that should give you more time.

 

If you build later, then I think the key to risk management will be to build as quickly as is humanly possible after theirs.

 

I think that you will need to accept certain constraints to join the two together. Roof profile at the boundary sounds like one of these to me. THe foundation are surely best built together if you so need? I am not sure whether sticking a bit of extra foundations on the side is a major Planning Sin; I don't see it, myself.

 

I would build the full strip foundations and cover it up if I want to keep it quiet. Alternatively if you wanted you could temporarily call it something that does not need planing permission, such as a patio base, that happens to be built to extension standards. THat would need professional advice; my personal opinion is that it might work as a defence.

 

One issue is that you may need to decide how you will both be managing a 300mm wide gap, when it gets full of gunk in a few years. I hate gaps that I cannot get down myself, and 4-5m is a very long pole.

 

Ferdinand

Edited March 7, 2018 by Ferdinand

[ToughButterCup]

You are in familiar territory. The end of one thing and the beginning of another.  I hope these two resources will be of some help.

 

You might like to have a look at this resource (The Party Wall Act )

Here's a link to the official  Explanatory Booklet

I suspect you might have already done this, but if you haven't......

 

Welcome by the way!

Ian

[ProDave]

As I see it, you just need to give permission to the neighbour to build the wall on the party line (half on his garden half on yours) in return for an agreement that you can join onto it when you are ready to build your own extension.

 

The obvious question will be is his extension the correct size for what you have in mind for your own?

[Brickie]

Re the footings you could possibly get the neighbours to stop at the front junction with a boot detail & starte rebars coming into your property. 

[Chris S]

Many thanks for all of your responses.

 

As much as we would love the extra 300mm, and as much as there are ways and means of making it happen, we have decided that the risks involved and the extra stress that it will cause are too great for us to be the ones pushing for it to happen in not enough time.

 

We will however raise the question of managing the gap with the neighbours and at the same time may well mention that had timing been right we could have built a shared wall. If it turns out that they want to pursue a shared wall they would have to be willing to delay their build and adjust their design whilst we get our design and agreements in order. That would take the pressure off and mean that we have the time to manage the risks properly.

 

I'll keep you posted...

 

Thanks again

Edited March 7, 2018 by Chris S

[PeterW]

I’m assuming both of you will have sorted a party wall agreement as you will be digging within the 45 degree angle of each other’s foundations ..?? 

 

Best to get that sorted ASAP so there is no come back 

[ProDave]

I don't see why they need to delay their build just so they can move the wall 300mm?  Or do you think that change would force it to go through planning again?

 

It would be a barmy solution of you both stepped your walls in and left an unreachable, unmaintainable gap between them.