Rear extension into a garden with a swimming pool

[Sidd]

Hi Community.

I am planning to obtain a planning permission to build a rear extension in my detached home. The complication is that the boundary of the extension will be within 'zone of influence' of a water retaining body i,e a swimming pool. The max depth of the pool is 1.5metres and the extension will be around 2.5metres from the boundary of the extension. I have had builders mention that the works could be complicated on account of 1. deeper foundation required 2. access issues. I also forsee building regulation requirements to be tough. I have attached a (blurry) top view showing the property and have tried to indicate where the extension would be build.
What are my options to reduce the complexity of the extension (and as result reduce build cost) ? 

Is access going to be big issue ? 

What are the best options to cover the pool to stop debris from coming in ?

 

[Redbeard]

59 minutes ago, Sidd said:

Is access going to be big issue ? 

Maybe. I cannot see a side path, but maybe there is, on the RHS. Can you get down there all the stuff you need? If it is a narrow path then there may be a lot of double-handling; for example pallets of bricks need to be stored at front and barrowed in small loads. Etc. etc x lots.

 

You need an SE to design footings which will 'cut the mustard' with the least possible digging and impact on the pool. @Gus Potter may be along later.

 

What is the green bit next to the proposed ext'n? Is it a hard-standing or the roof of something else?

1 hour ago, Sidd said:

What are my options to reduce the complexity of the extension

A lot may depend on whether you are having this wholly built by mainstream builders, or you are having significant input yourself. One person's 'fiddly' is another's 'joy of detailing'. And again, in terms of cost reduction, if you are providing say 75% of the labour after footings, and you are good with blocks, then building in block may be the answer. If you are good with wood, then TF... etc. So, is this a 'contractor job' or are you getting your hands dirty? The more detail you can give re 'variables' the more informed an answer we can give.

 

I am visualising v deep footings next to the pool (ooh err!) but I am not a Structural Engineer.

[Sidd]

4 hours ago, Redbeard said:

Maybe. I cannot see a side path, but maybe there is, on the RHS. Can you get down there all the stuff you need? If it is a narrow path then there may be a lot of double-handling; for example pallets of bricks need to be stored at front and barrowed in small loads. Etc. etc x lots.

 

You need an SE to design footings which will 'cut the mustard' with the least possible digging and impact on the pool. @Gus Potter may be along later.

 

What is the green bit next to the proposed ext'n? Is it a hard-standing or the roof of something else?

A lot may depend on whether you are having this wholly built by mainstream builders, or you are having significant input yourself. One person's 'fiddly' is another's 'joy of detailing'. And again, in terms of cost reduction, if you are providing say 75% of the labour after footings, and you are good with blocks, then building in block may be the answer. If you are good with wood, then TF... etc. So, is this a 'contractor job' or are you getting your hands dirty? The more detail you can give re 'variables' the more informed an answer we can give.

 

I am visualising v deep footings next to the pool (ooh err!) but I am not a Structural Engineer.

Thanks, appreciate it. 

 

Access - 

There is a path (typical garden side door) Think a mini digger would pass

 

What is the green bit next to the proposed ext'n? Is it a hard-standing or the roof of something else?

That is existing structure with roof terrace. From a planning perspective, this would actually be a side extension.

 

is this a 'contractor job' or are you getting your hands dirty?

Contractor job but given the uniqueness of the situation I want to ensure I understand and guide them. 

I have a SE but again struggling to see expertise that this needs. (maybe its me)

 

Out-of-box thought - Should I consider a steel extension to remove need for foundations. Say Vita Modular.

 

Again - thank you.

[Redbeard]

 

46 minutes ago, Sidd said:

Out-of-box thought - Should I consider a steel extension to remove need for foundations. Say Vita Modular.

 

 

I assume you mean 'remove the need for conventional deep strip foundations...'. Even with steels you still need foundations - just fewer of them, insofar as you only need a footing where a post hits the ground (probably - ish).

 

- Installation of new structural beam supports with associated foundations as required

 

50 minutes ago, Sidd said:

I have a SE but again struggling to see expertise that this needs. (maybe its me)

 

There are, at very least,  2 bits you need the SE for, I'd say: 1. To tell you how you make the pool 'stand up' while you almost undermine it with your footings and 2. To tell you what you need to make your extension stand up. Oh, and 3. You need his/her PI insurance....

[Sidd]

5 hours ago, Redbeard said:

There are, at very least,  2 bits you need the SE for, I'd say: 1. To tell you how you make the pool 'stand up' while you almost undermine it with your footings and 2. To tell you what you need to make your extension stand up. Oh, and 3. You need his/her PI insurance....

Thanks again. Good point about PI - though I fear scaring him away ! 

One final question - If I retain the structure of the sunroom as-is (constructed in 1970s) and essentially treat extension as a separate room and only two new walls to build and add a roof. Devil in details but theoretically does it reduce cost/risk ?

 

Cheers.

[Nickfromwales]

What’s the timelines? Pool went in before the ‘side’ extension or after?

 

Do you know the size of the excavation that occurred for the pool, and ground conditions?

 

Is the new extension to be 1 or 2-storey?

 

You may be able to do a piled (screw vs percussion) foundation to completely remove the need to excavate, other than for a foul pipe if there’s need for drainage. You’ll need geotechnical survey doing by the foundation contractor or independent to see if that’s an option, plus you’ll need to know what services lay beneath, historical records for mains sewers / gas / water and so on.

 

I’d be asking a ‘pool expert’ if you’re better off emptying the pool during these works, or half emptying it, or leaving it full etc. That will likely be a good SE, one who’s done pools before. I have a very good SE I can share details of who’s very well versed in ICF / pools / basements, PM me if you get stuck.

 

For a covering, do a good job as you don’t want any damage to the pool whatsoever. 4x2 timbers across the width and 18mm OSB sheets to cover the pool. Make some uprights at each corner and midpoints as necessary with hazard tape strung between them to act as a guard rail, and a BFO sign saying not to walk on it and swimming pool below etc.

[saveasteading]

In Engineering terms this isn't as worrying as you might think. Water in the pool weighs 1t/m3. The ground around it is  heavier.  I would expect the new foundations NOT to be deep so that the pool is unaffected. 

Are there technical  drawings of the pool walls?

 

But construction is the issue, and the need to not damage the pool.  So standard or shallow foundations would be the aim.*

 

Keep the extension design simple, such that it can all be carried or barrowed.

Excavation may have to be manual.

 

The very biggest concern would be that any future issue with the pool would be blamed on this work.  But if the pool is your own, then that isn't a worry to you.

 

An SE will handle this readily, and will also advise on how to build it so the pool is unaffected.

Your builder has to be careful.

@Gus Potter may agree or disagree.

 

* loads do not disperse at 45° but it's a decent rule of thumb. If you know where the pool footing is, and draw 45° out from there,  then do the same for your extension, if neither line cuts through the other structure then it's looking OK in Very, very approximate terms.

 

 

 

Edited 1 hour ago by saveasteading