ᐅ Searching for Materials for a Garage Floor Slab

Hello everyone,

I am currently planning a larger garage in front of the house and will be doing all the work on the garage myself. The garage will be built from wood and is quite large (about 9 x 7 meters (30 x 23 feet)).

Accordingly, the concrete slab will also be somewhat larger, so the potential savings through self-labor are also quite significant.

Briefly described: The insulation boards have a “finished” formwork on the outside and are placed together as the outer edge, then “glued” together with tape. Then the interior membrane is laid out. Above that, there is a vapor barrier and another layer of insulation. Then the concrete is poured. (If necessary, the piping and underfloor heating will be installed on the second insulation layer.)

The concept seems wonderfully simple to me. Since I am currently working on the initial cost estimates, I searched for the material online and found various suppliers who also present very similar materials on their websites. Unfortunately, I cannot find the material in online shops nor any price information. Perhaps I just lack the right search terms.

Does anyone have material recommendations and sources including prices that I can use for my calculations?

Many thanks!

Best regards

- Why insulation?
- Why underfloor heating?
- Have you already planned external insulation?
- Are you clear about the earthworks?
- Are you also clear about routing pipes into the garage?
- I don’t understand the purpose of insulation, vapor retarder, vapor barrier, and insulation in that order
- Underfloor heating as thermal activation of the concrete core, since underfloor heating is usually installed in the screed
- The specific material you mentioned is unknown to me

- Why insulation?

Both for thermal insulation and because the overall concept is straightforward and easy to implement. The panels provide a good and clean base that allows for smooth further work with the concrete.

- Why underfloor heating?

The building is intended to be heated afterward. Mainly in the upper part, under the pitched roof, where an office will be set up. However, the lower part should also be able to be heated or cooled with the underfloor heating depending on the use case. The additional cost for the underfloor heating is negligible.

- Has external insulation already been planned?

Yes, that is quite simple as well. The building stands on 18cm (7 inches) posts, so 18cm (7 inches) of mineral wool insulation fits in between. Cost-wise, it is also negligible, so that will be added to the wall. The same applies to the vapor barriers.

- Are you clear about the earthworks?

I don’t have to dig very deep at the planned location because the soil here consists of clean sand. The sand layer starts at about 30cm (12 inches). I will probably need to dig down 50cm (20 inches). So, 2-3 days of excavator work. It’s fun every now and then.

- Are you also clear about pipe and cable entry into the garage?

That is also quite simple. The main house is about one meter (3 feet) away from the planned garage. The utility room is conveniently aligned. There is an empty conduit free here (110mm (4.3 inches) PVC sewer pipe) that will carry hot water, cold water, 230V power, 400V power, and the underfloor heating supply. There is no need to involve the utility company for this, which would not make sense.

- I don’t understand the purpose or order of insulation, interior membrane, vapor barrier, insulation

I can’t help much with the details here either. The company Fjortherm installs these floor panels in this way, so there must be a good reason for this sequence.

- Underfloor heating as thermally activated building mass, since underfloor heating is usually in the screed

The slab shown in the video contains only the “screed concrete.” There is no additional concrete layer, so the underfloor heating is indeed embedded in the screed.

- The specific material you mentioned is unfamiliar to me

I found something similar.

But as mentioned, I have no “shop” or price information.

The alternative that comes to mind is, of course, to build strip foundations. In that case, I would have to forgo insulation and underfloor heating and leave the lower part of the building uninsulated. That makes a huge difference in cost. I would like to quantify this exactly to see if the investment is worthwhile.

PinkyPinky schrieb:

The building is going to be heated afterwards. Mostly the upper part, meaning under the pitched roof, where an office will be set up. However, the lower part should also be able to be heated or cooled with underfloor heating, depending on the use case. The additional cost for the underfloor heating is negligible.

I thought you were building a garage and not a living space? That makes it even more interesting – please be sure to comply with the building energy regulations everywhere.
And if the extra cost is negligible, are you planning to buy a new heat pump or can the existing one simply heat an additional 100 sqm (1076 sq ft)?

PinkyPinky schrieb:

Yes, that is quite simple as well. The building rests on 18cm (7 inches) joists, so that leaves room for 18cm (7 inches) of mineral wool insulation in between. Cost-wise also negligible, so just put it in the wall. Same applies to the vapor barriers.

So basically, the whole construction cost is negligible?

PinkyPinky schrieb:

Also quite simple. The main house is located one meter (3.3 feet) away from the planned garage. The utility room is perfectly positioned. There is an empty conduit here (110mm (4.3 inches) PVC pipe) that will carry hot water, cold water, 230V electricity, 400V electricity, and the underfloor heating system over. No need to involve multiple utilities separately, that would be pointless.

LOL. Does the wastewater just evaporate then? Just a small side note.

PinkyPinky schrieb:

The company Fjortherm installs these floor slabs this way, so there must be a reason for it.

Then you should ask them. Many things have their reasons, but not everything is suitable for every project.

PinkyPinky schrieb:

The obvious alternative would be to build a strip foundation. In that case, I would have to forgo the thermal insulation and underfloor heating and leave the lower part of the building uninsulated. That makes a huge difference in cost, of course. I would like to quantify that precisely to see if the investment is worthwhile.

Always remember you need an architect and a building permit / planning permission. That means you must comply with all building energy regulations. I would recommend finding a planner who specializes in supporting DIY builders.

PinkyPinky schrieb:

The floor slab as shown in the video only contains the "screed concrete." There is no additional concrete layer, so the underfloor heating is embedded in the screed.

That is thermal activation of the concrete core, not screed. Also known as a “Swedish slab.” This term might help you with your research. Cost-wise, it is not far off from a “standard” construction.

I thought you were building a garage, not a residential unit? That makes it even more interesting – please make sure to comply with the Building Energy Act / building energy regulations everywhere.
And if the additional costs are negligible (buy a heat pump, or can the existing heat pump simply heat an extra 100sqm (1,076 sq ft)?

The building will be a mix. Garage on the ground floor, living space above. Rather basic, since it’s only supposed to be an office, possibly including a small bathroom and kitchen.
Yes, the heat pump was already planned for this building and it can handle that.

So basically, the entire construction cost is negligible?

I wouldn’t go that far. The cost for the wood of the building itself (~ < 20,000€) or the roof covering (3,000–5,000€) is much more significant than the insulation material.
For mineral wool insulation of the required thickness, I’m looking at about 1,200€. Although there are many of these small expenses that add up to a large portion, that is not really the topic here.

LOL. The wastewater just evaporates then? Just a little remark.

Don’t be so arrogant. Apparently, I forgot to mention wastewater.
Like any good German, I of course carry it to the street in buckets.
The effort to lay a 1kg (likely 1kg is a typo for a common pipe size, but based on instruction just keep as is) pipe and connect it to the existing sewage line is rather small. But this is also not really part of the actual question.

That is concrete core activation. Not screed. It’s also known as a "Swedish slab." Maybe that term helps you with your search. Cost-wise it’s not far from a "normal" floor construction.

Yes, exactly. I’m familiar with the term "Swedish slab," and it applies here. I’m looking for materials for it. Unfortunately, suitable building materials are not easy to find online. But I also can’t imagine that the few companies that install Swedish slabs use this material exclusively.

PinkyPinky schrieb:

Now don’t be so arrogant. Apparently, I forgot to mention the wastewater.
Like every good German, I naturally carry it in buckets to the street.

Not arrogant. But if you knew the kind of questions that come up here. And when someone wants to build a garage and it ends up being a “house,” you can easily see how such a detail gets overlooked.
Pipe under the building permit / planning permission. Penetrations. Adjustments to the inspection chamber. Plus rainwater. And so on.
It’s not a minor issue. That’s why the “LOL.”

PinkyPinky schrieb:

Yes, exactly. I’m familiar with the term “Schwedenplatte” and it applies here. I’m looking for materials for it. Unfortunately, suitable building materials are not easy to find online. But I can’t imagine that the few companies that install Schwedenplatten use this material exclusively.

Just do it the classic way. Some wooden planks and stakes and pour.