Casting slab over geothermal borehole

[crazytok]

Yes, that sounds funny! 😬

But here's the thing, we have our borehole for geothermal heating drilled right outside the entrance of the house. And now we want to extend our hall which would result in us pouring a slab over it!

Not optimal in any way, but what's the alternative? Does it matter? What kind of access do you actually need to the borehole and why? Is there a smart solution, like pouring around it and leaving 1x1m open and putting floor joists there instead?

Or just pour over the hole and forget about it? 😂

 

[MathiasS]

.....you might need to change the hose? Flush the hole maybe? Seems boring to do in the hall.

 

[jonaserik]

Depending on what temperature the heat pump (VP) creates out on the brine circuit (KB), if it becomes many degrees below zero, the connections/welds on the hoses down can freeze and it can leak. It's not the first time this has happened. So it's advisable to have access to everything at the borehole, nothing happens down in the hole, hopefully, and it's rare.

 

[datja]

Yes, that sounds funny! 😬

But here's the deal, we have our hole drilled for geothermal heating just outside the house entrance. And now we want to extend our hallway, which would result in us pouring a slab over it!

Not optimal in any way, but what's the alternative? Does it matter? What kind of access do you really need to the borehole and why? Is there any smart solution, like pouring around it and leaving a 1x1m open and placing floor joists there instead?

Or just pour over the thing and forget about it? 😂

In 2012, we did (almost) like you. Our extension could only go in one direction. The geothermal hole turned out to be located right under the new exterior wall, directly under the lecablock and concrete elements. We tried to provide access to the hole from the outside with a concrete beam instead of the usual elements, but you can never access the hole directly from above.

I would try to arrange some form of access, but of course, it depends on what kind of room it will be above the hole.

 

[Thomas_Blekinge]

You can choose between two options:
1. Cast above the well. If there are problems with the well in the future, you abandon the borehole and drill a new one a bit further away.
2. Drill a new one elsewhere already now.

Advantage 2: you can choose the time and avoid waiting for the drilling company when you have problems. And you can drill deeper than what you have today if it happens to be too shallow.

It is also likely cheaper to drill a new one now than in 10 years.

 

[crazytok]

…..you might need to change the hose? Maybe rinse the hole? Seems boring to do it in the hall.

Sounds comfortable… 😝

So… what's your suggestion instead then?

 

[crazytok]

Depending on what temperature the heat pump creates for the brine, if it gets too cold, the connections/welds on the hoses can freeze and it may leak. It's not the first time it's happened, so the possibility of accessing everything at the borehole is recommended. Down in the hole, hopefully nothing happens, and it's rare.

What do you think about casting around and having a regular floor joist 1x1m where the hole is? It's tedious/annoying to have underfloor heating and tiles above, but what else can you do? 🤷‍♂️ It still seems easier to remove several tiles and cut the underfloor heating hoses and splice them in the future if you need to get through to reach the hole, rather than having to dig up and remove half the tiling/masonry on the outside of the house to access and dig a new trench for the geothermal loop.

The borehole is also only 8 years old.

 

[crazytok]

In 2012, we did (almost) like you. Our expansion could only go in one direction. The geothermal hole turned out to be located just under the new outer wall, straight under leca blocks and concrete elements. We tried to manage access to the hole from the outside with a concrete beam instead of the usual elements, but you can never reach the hole directly from above.

I would have tried to arrange some form of access, but of course, it depends on what kind of room will be above the hole.

It will be a hallway floor right above! So potentially casting around and having a regular 1x1m floor beam at the borehole could be a solution. Even though it will be tedious to remove tiles and everything underfloor to get access… 😬

 

[crazytok]

You can choose between two things:
1. Cast above the borehole. If there are problems with the borehole in the future, you abandon it and drill a new one a bit away.
2. Drill new elsewhere right now.

Advantage 2: you can choose the time and avoid waiting for the drilling company when you have problems. and you can drill deeper than you have today if it's shallow.

It's probably also cheaper to drill a new one now than in 10 years.

If you choose option 1, how do you access and lead the new loop to the pump under the floor?

 

[Maxwells demon]

We have cast over the energy well for the expansion. I spoke with my heat pump installer about how many jobs he has been on where it was necessary to perform any service in the well. Never with welded connections, he said. He has been on a few cracked PRK cases, but he says that PRK is not serious.

 

[jonaserik]

What do you think about casting around and having a regular floor joist 1x1m where the hole is?
It's boring/hard to have heating coils and tiles above, but what the heck should one do? 🤷‍♂️ It still feels easier to remove X number of tiles and cut off the floor heating coils and splice them in the future if you need to get through to reach the hole, rather than having to dig up and remove half the tiling/masonry outside the house to access and dig a new trench for geothermal heating coil.

The borehole is also only 8 years old.

If you are going to have tiles and GV, then it is probably best to cast over, first check if there are welded angles or connections, the latter are troublesome.

 

[MathiasS]

I think it sounds convenient… 😝

So… what’s your suggestion then instead?

You should at least build a large inspection hatch. It just seems too silly to embed the stuff.

 

[datja]

What do you think about casting around and having a regular floor joist 1x1m where the hole is?
It's boring/tedious to have heating coils and tiles above, but what the heck can you do? 🤷‍♂️ It still feels easier to remove X number of tiles and cut off and splice underfloor heating coils if needed to access the hole, rather than digging up and removing half the tile setting/masonry outside the house to access and dig a new trench for a ground source heat pump loop.

The borehole is also only 8 years old.

I would have left a 1x1 m defect in the slab directly over the hole and filled it with insulation (think of it as an extremely minimized crawl space with very thick walls). The radon protective plastic through the void. Notches at the hole's top edge for removable concrete beams on which you can place floorboards.

 

[nino]

It depends a bit on how big an extension you're planning and what the plot looks like.
One solution might be to dig away 50-100cm above the hole and to the side.
Cast edge beams, build up with masonry and make a wooden floor structure, as well as a hatch down, or a smaller door from the outside.