Self Build in the UK!

[jaseypk]

Morning Everyone!

I've been silently reading your forum in the background, and absorbing almost all of Youtube's self build content for about. year now, and now the time has come. The council have granted us permission to start, so here I am!

I'd like to say thank you to all those who post helpful content on here - it really is appreciated even by the secret readers like me (richie967 and Teapot1)

So I've just started to mark out and clear the area for a pool in my garden in the heart of Yorkshire, England:
- a 4m x 2.5m pool, approx 1.4m deep, constructed from blocks on a concrete base, insulated, with the surfaces rendered and tiled. I don't fancy a liner, and I prefer the look of tiles all over to painted.
- Pool will be sunk into the ground 1m, then raised above ground by the remaining 40cm. The reason for this is we have a young child, and a hyperactive dog, and I don't want either of them falling in accidentally! It'll also help keep all the leaves and blossom from a nearby tree out (I hope).
- I think I'm 'opting out' of a ground drain and just using a single skimmer as the pool isn't very big and the online consensus seems to be that ground drains are just a source of problems
- I wanted it heated to be usable all year round (ideally 30'c + all year... 35'c if possible!). The dream is to float in the pool with a beer when there is snow on the ground
- Target completion date is August the year - hopefully gives me plenty of time. Obviously if it's ready sooner, even better!

I think I've got plenty absorbed knowledge for construction for the moment while I dig a hole, but I want to build a pit at the same time to house as much equipment as I can. So that said, I need to work out how I'm going to heat this pool to 30'c in all weathers from 0'c - 30'c. I'd like to use the most efficient method of course, which I understand is a heat pump. But - I can't seem to find any resource on how to calculate the size heat pump I need to cater for these needs. I'm also presuming the heat pump will need to be above ground, surrounded by fresh air and not in a sealed pit underground.

So, first questions to get me started:

1) Is a heat pump the best course of action for an all year round 30'c pool, with ambient temps of 0-30'c? If not, what is?

2) How do I calculate what size heat pump I need? kWh to 'units' means nothing to me right now, so I may need someone to explain the maths to me.

3) Any preliminary advice while I start digging is greatly appreciated. I've never built a pool before, but I'm fairly handy with construction and plumbing so I'm hoping it won't be too much of a headache!

Thanks all!
Jase

[Teapot1]

Answer in the morning, too late tonight.

[jaseypk]

Answer in the morning, too late tonight.

Morning, apologies but I’m presuming you’ve forgotten to reply.

Digging progress is going slower than I’d have liked but we’re getting there. Somehow I’ve incentivised a ‘digging party’ for a few friends over the next few weeks so that should finish it off!

[Teapot1]

Hi Jase, I did indeed forget to post.
1. Heat pump is the most economic way of heating but as temperatures drop so does the efficiency so could get expensive compared to gas. That also said being in a warm pool at say 27c in cold weather is when you get out its bloody cold especially if there is a breeze!
2. Wouldn't go less than 12kw, might be a bit of overkill but better to have some in reserve. Gas heats the pool quickly, heat pumps long and slow. A good thermal cover is an idea. A lot of the heat loss depends on drafts over the surface of the water.
3. The foundation slab should be wider than the pool by a min of 300mm all round and deeper at the edges to make a stronger slab, I am sure you would have seen examples on the web whilst you have been researching.
Hopefully you have read my many posts on variable speed pumps and Dryden Aqua's AFM ng filter media.

[jaseypk]

That’s great, thanks. I had seen you’d mentioned before in another post about enlarging the slab, so I’ll make sure my hole is bigger accordingly.

I had thought of the winter running and for this first year it’ll be a bit of an experiment I guess. See how efficient it isn’t and decide if The costs of running through the icy season are worth it or not.

I’ve not read about the variable speed pumps or filters, but I’ll take a look now, thanks!

[jaseypk]

Hole has been dug out, approximately 200mm of compacted type 1 hardcore is now in the hole too! It’s been heavy lifting month and I’m so glad it’s over.

I’ve got the rebar for the concrete slab and booked a date for the concrete but I’m currently deliberating on insulation under the base.

As the compacted hardcore isn’t like sheet marble, it’s therefore going to have a few air pockets if I laid 50mm XPS on top. I’m then concerned that if I pour 200mm concrete on top, that these air pockets will be weak points. Or, will the XPS crush or conform to the compacted base contours?

Will insulating the base actually make enough difference to make it worthwhile? It’s not the financial loss I’m concerned about, it’s the integrity of the concrete slab if there are air pockets between it and the hardcore.

Thanks in advance!

[Teapot1]

Have you blinded out the type 1 with sand to fill any voids/air pockets? Extruded insulation comes in different grades from around 15 metric tonnes to 40 tonnes per sq metre so you'll be fine. I would also say 150mm of concrete would be fine and may allow you to increase the XPS a bit more.

[jaseypk]

Hi Teapot, I’d not thought about sand - good idea! I’ll do that to level as best I can. I’ve gone with 6mm A142 rebar, but as with the internet I’ve now read more information that states this may be too thin!

I’m so worried about this concrete base you wouldn’t believe!! I’ve got 2 weeks before concrete arrives so I’ve got time to adjust levels and get the rebar just right (500mm overlaps and I’ve got some 10mm rods to create rising L angles for the blockwork.

Do you think 200mm concrete is a completely unnecessary overkill then? My logic right now is better safe than sorry! The pain of a cracked base is more than the cost of a bit of concrete to me!

Thanks again!

[Teapot1]

Pools I have built are all 150mm base. Except under the walls which I go thicker on to 200mm or more depending on the ground sub soil. If the pool was larger say +10m long I may increase the thickness. My neighbours pool built by another company got their maths wrong and its about 1 pebble thick on the far side. Depends on the sub soil of course as well.

[jaseypk]

Okay great, thanks! Our subsoil is pretty much pure sand. Zero clay, zero rock. Drains very well, but I presume is also the cause of subsidence issues on most houses in our area, so ours like many has had to be underpinned after movement 60 years later!

I’ve opted for pumped concrete which is metered in, so they can just pump until it’s up to level - no wastage and won’t undermeasure! Also saves me the effort of levelling myself as these guys will do that for me (I’ve used them before).

Thanks again - advice and help is always appreciated!

[Teapot1]

Sounds like 200mm is the better idea. Good luck with the concrete and keep us informed.

[jaseypk]

Concrete is in and had a good week to go off to allow me to start building on it! It’s looking good - nice and level, also super smooth with my rebar poking out nicely for the blockwork to slot onto (hopefully).

I’ve got a delivery of all the blocks, sand, cement, pea shingle and rebar this Friday so will start building the walls then and filling with concrete every course.

I do have one question though please as it’ll need factoring in when I’m building. Pipe size! I’ve done some googling and “swimming pool steve” seems to know a bit, and is making me think that for a small pool which will hold roughly 13,000 litres, it needs a 1.25” pipe to be most efficient, coupled with a suitable sized pump and filter. Would you say this is correct? I don’t want to undersize, or oversize where I’m leaving holes for my inlet(s). Now is also the time to decide if two inlets are better than the one I had planned!

I’m also having a little trouble finding a pump small enough to meet my needs - most pumps I see seem to have a turnover rate for my pool in excess of 3 or 4 times per 24hr running. Certikin do mini pumps down to 0.25hp with 1.5” connections on them - again any advice on this would be greatly appreciated! I know Teapot, you’ve mentioned variable speed but this may have to be a future upgrade due to cost.

I’m taking the build day by day, ordering materials as we need to save storing them out in the elements until needed - so right now it’s building and preliminary plumbing.

Thanks!

[Teapot1]

I can't comment on what swimming pool Steve says as I haven't watched that video, if you point me to it I will take a look. That said, those from across the pond have a tendency to oversize their pumps, undersize their filters and possibly Steve is undersizing the pipes as well. For 1.5"/50mm the maximum efficiency is around 8m3 per hour, 2"/63mm around 17m3 per hour (wall thickness of the pipes will vary this somewhat) my pool 12000 ish of the US gallons 42m3 in metric filters at about 7m3 per hour which is very close to the efficiency of 50mm pipe so 1.25" ??? Not unless you want trouble connecting everything up. Now thats just on filtration, we need about 3 times that flow rate to backwash a filter so how does Steve figure that works? Ah he believes cartridge filters are best, he is of course wrong on that as well. Just as Steve is wrong about liners and how long they last. He has been told this many times and whilst he does try to move towards a lower energy model he doesn't really understand.

As to pumps, 3-4 turnovers (24 hour filtration brings the best water clarity and quality) Certikin (spit) its still an energy guzzling pump, designed with an impeller for priming above the waterline setups so not max efficiency. Send me a private message and I will try to help you.