Owner Build in the UK - Under Floor Insulation Question

[richieb123]

Hi Forum,

I have a question on a small pool I am building in my garden in the UK. It is more paddling pool sized. 5m x 3m x 1.2m internal. It will be constant depth and heated.

I have dug the hole - 6m x 4m x 1.6m by hand. Which took 3 months, as most of it was rock. And I am planning on insulating it with 50mm XPS insulation. I have received a lot of conflicting advice. Can the insulation go under the entire slab, or should it go on top of the slab?

The Slab is 6 inches (150mm) thick with a393 steel mesh in it. The walls are 12 courses of blocks laid on their side.

I have shown a picture of the excavation, a close up of the slab and insulation, and a picture of the pool in its entirety.

Thanks In Advance, Rich

 

[Matt F 1]

Welcome to the group.....

First off ground temperatures don't fluctuate all that much, below the frost line. So you might want to just insulate the perimiter of the floor and the walls.

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[richieb123]

Hi Matt, Thanks for the information. As we live in the UK im guessing that I always want the water temperature of the water to be higher than the ground temp, so thought id insulate it as much as possible, so when heating it up to temp i don't need to heat the surrounding soil , just the water, walls, and slab i guess. I believe we also have regulations that mean that the walls and floor should be insulated to allow less than 0.25 wh/m2.

I guess I have 3 options...

Option 1 - Lay insulation across the entire Slab, so the insulation completely surrounds the pool structure, is this worth it? This is also probably the easiest option. As only one lot of concrete mix is required.

Option 2 - Lay the insulation only under the water. Would there be heat loss through the walls into the surrounding rock?

Option 3 - Pour the base straight onto the chippings, then build the walls, and add the insulation on top of the slab then some screed on top of the insulation? Or maybe the screed isnt even needed? As the liner can go straight on top of the insulation?

Questions are:

1. Do you see any structural issues with insulating under the entire slab for ease? it seems to be ok to do as long as your XPS has the required compressive strength.
This example seems to show that insulation does get placed under walls. And in the majority of cases, insulation gets placed under the slab as opposed to on top,

2. Is insulating a pool beneficial? i've already purchased 24 sq/m for the entire base....! Greenguard GG300 XPS 50mm. 300kpa. closed cell. I've also just read that only 10% of the overall heat loss is through the walls and floow through convection, whereas the majority of heat loss is evaporation. Making me think ive wasted £350 on insulation!

Thanks for the warm welcome!

Rich

 

[Matt F 1]

Picture 2 or 3 would work but you will loose more heat from evaporation off the top. Concrete is not a good conductor of heat. So once it's warm it will stay warm.

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[richieb123]

Thanks for the information Matt. Maybe I've been placing more importance on insulating the base and the walls than I should have been! I've previously bought 24 sq/m of insulation. Enough to cover the entire base even under the walls. Obviously this is the easiest option, is it best avoided? As the walls really should be on concrete that has no insulation under it?

 

[Matt F 1]

I don't know what your building codes are in the UK. But you might need a bigger footing under the walls to support the weight. I would ask your city or area building department.


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[richieb123]

Hi Matt, I finished the pool. And made a short video, it's been brilliant!

 

[Matt F 1]

Rich, Just love the video, and the pool looks great.
You're a man with some skills!!
Enjoy.....

M

 

[sktn77a]

Great job!