ᐅ Mill the subfloor for underfloor heating or install a new screed?

SaniererNRW123 schrieb:

That is actually a proper insulation – it definitely does not replace insulation of the basement ceiling. You can hardly go with less insulation (both thickness and quality). Either use rigid PUR insulation directly (although I would still find that too thin) or simply install 8cm (3 inches) PUR under the basement ceiling.

Thank you for the quick and helpful response! Was that irony, or is insulating the screed really a sensible approach? Does the PUR insulation refer to the basement ceiling? Can this be done as a DIY project with some skills, and what (material) costs should I roughly expect? I quickly looked up some offers, mostly for underfloor heating, with both PUR and PIR. According to initial research, PUR apparently has a more balanced material distribution than PIR.

SaniererNRW123 schrieb:

Is there a heating load calculation to confirm that the house will be heated efficiently with these data (heating costs)?
For 140 sqm (1506 sq ft) and 12.5cm (5 inches), about 950 meters (3117 feet) of tubing will be installed (standard underfloor heating pipes are typically 16/2 mm or thicker). Then 11 loops are sufficient.
Classic underfloor heating with 10cm (4 inches) pipe spacing (more effective due to lower flow temperature possible → better suited for future heat pumps) and 16/2 mm pipes will obviously deliver much better heating performance.

I would remove the screed and look for a plumber who allows owner installation of the underfloor heating pipes (pipe stapling). You can definitely find one via online platforms or marketplaces.
Commission the heating design calculation externally (e.g., Heckmann).

We do not have a heating load calculation. Is this recommended? And if yes, does it require an on-site visit, and what costs should we expect? Perhaps these are also eligible for subsidies under the BAFA heating renovation program?!

Is it even possible to use larger pipes with milled underfloor heating? What exactly do you mean by "950m tubing" and 16/2 pipes?

We have already considered installing the underfloor heating ourselves and have even received initial offers for this. I have looked into it and found many different systems for (new) underfloor heating installations. Recently, I also came across systems by Schlüter that include uncoupling mats (name: "Schlüter®-BEKOTEC-THERM"). Have you heard of these? They seem particularly suitable for low build-up heights. But hopefully, that will not be much of an issue for us.

FCBenne04 schrieb:

Thanks for the quick and helpful response! Was that irony, or is insulating under the screed really effective?

Sorry, I missed a "k". It’s a basic, standard insulation. While it’s better than nothing, it doesn’t seriously prevent heat loss from the basement.

FCBenne04 schrieb:

Are you referring to PUR insulation on the basement ceiling? Is it possible to do it yourself with a bit of skill, and what approximate (material) costs should one expect? I quickly searched online and found various offers (some for underfloor), some with PUR and some with PIR. From initial research, PUR seems to have a more balanced distribution of materials compared to PIR.

PUR/PIR refers to both sides of the ceiling. You can install it under the screed and/or on the basement ceiling. The installation is straightforward—just foam adhesive sprayed and stuck to the ceiling (possibly supported temporarily with cheap props). You only need to be a bit creative if there are pipes or conduits on the basement ceiling.
Since you mentioned NW as your federal state and your username sounds like you are from the Ruhr area, I recommend a visit to Nettetal for insulation materials. They have seconds-grade products there, which are more than sufficient for basements or similar uses (I visit there quite often).

FCBenne04 schrieb:

We don’t have a heating load calculation. Would that be advisable? And if yes, does it require an on-site appointment and what costs are involved? Maybe this could even be subsidized under the BAFA heating renewal program?!

It is definitely recommended because it helps you properly size your heating system and underfloor heating (including hydraulic balancing). On-site? No, it can all be done online or by email.
The costs are reasonable—as far as I know, also eligible for subsidies. For example, something like this—you even get the underfloor heating layout plan included.

FCBenne04 schrieb:

Is it even possible to use larger pipes with a milled underfloor heating system? What exactly do you mean by "950m tubing" and 16/2 pipes?

I believe milled underfloor heating systems only use small-diameter pipes. In your case, about 950 meters (yards) would be installed. Larger pipes, like those used in a “conventional” underfloor heating system, typically start at 16mm diameter (wall thickness of 2mm). These allow significantly more water flow, enabling lower supply temperatures.
At a pipe spacing of 12.5cm (5 inches), you’d need about 950m of 14x2 pipe. If you reduce the pipe spacing to 10cm (4 inches), it goes up to around 1,230m. This is similar to having larger radiators that deliver the same heat at a lower water temperature as smaller radiators at higher temperatures.
Also, you have more heating water flowing through bigger pipes, but that means more heating circuits as well. I installed mine myself with pipe spacing often as low as 7.5cm (3 inches) in a 120sqm (1300 sq ft) old building—over 1.5 km (about 1 mile) of piping. In my opinion, the extra material cost is not a deterrent since it’s not much more expensive.

FCBenne04 schrieb:

We have also considered stapling the underfloor heating pipes and have even been offered this initially. I noticed there are many systems for newly installed underfloor heating. I recently saw systems from Schlüter with uncoupling mats (called "Schlüter®-BEKOTEC-THERM"). Have you heard of them? It seems useful, especially with low build-up height. Hopefully, that’s not a big problem for us here.

I’ve heard of them but never used them. Recently, I simply laid insulation on the floor, taped down a grid foil on top, and stapled the pipes directly to the insulation/foil. It’s labor-intensive but quick and doable without much prior knowledge.

If you install and staple it yourself, you have no warranty claims against anyone in case of damage.
They will always turn it around to say that you caused the hairline crack in the pipe yourself because you stapled it incorrectly or trampled on it like an elephant. 😉

Whether saving a few thousand euros (dollars) is worth it in the end depends on whether your floor ends up wet or not...

PS:
Almost everything in construction can be done without prior knowledge. But you are also responsible if things go wrong because you didn’t know how to do it properly or weren’t aware of the critical points that matter.

xMisterDx schrieb:

If you install and staple the pipes yourself, you have no warranty claims against anyone in case of damage.
They will always argue that you caused the hairline crack in the pipe yourself, either by stapling incorrectly or by stepping on it like an elephant 😉

Whether the few thousand euros saved in the end are worth it... that depends on whether your floor ends up wet or not...

PS:
Almost everything on a construction site can be done without prior knowledge. But if something goes wrong, that’s your own fault because you didn’t know how to do it properly or were unaware of the critical points that really matter.

Thanks, I wanted to add to this as well. Since I’m currently dealing with the same issue (stapling underfloor heating pipes). In the end, I had the heating engineer do it, precisely because of the warranty considerations. I could have saved about €1200 (around $1300) if I had done it myself, but any claims for defects or subsequent damages would have been void.

xMisterDx schrieb:

Almost everything on a construction site can be done without prior experience. However, if something goes wrong, it’s also your own fault because you didn’t know how to do it properly or weren’t familiar with the critical points that matter.

That’s exactly why you do it together with the heating engineer. You install and staple it yourself, but the heating engineer performs the pressure test and takes over the warranty. This is a very common procedure in construction. That’s also how I recommend it.
For my own projects, I do everything myself—at least then I know exactly who messed up. 😉

SaniererNRW123 schrieb:

That’s exactly why this is done together with the heating specialist. You install and staple it yourself. The heating specialist then pressure tests and takes over the warranty. A very common approach in construction. That’s how I also recommend it.
In my case, I handle everything myself – at least then I know who made the mistakes 😉

I had suggested the same. Mine refused. Either he installs and pressure tests, or there is no warranty. Seems like there are regional differences on this issue.