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How to Insulate 44m2 Concrete Slab Garage: Wool vs 5cm Foam, OSB Installation & Best Practices

chudy0321 13179 11
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  • #1 16951992
    chudy0321
    Level 9  
    Colleagues, as in the subject I have a garage of concrete slabs about 44m2 unheated wants to insulate it from the inside with wool between the columns and press OSB and I do not know if this is a good idea? Maybe push 5cm foam instead of wool, I don't know, I will suggest something
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  • #2 16952011
    barton21
    Level 26  
    Better steropian. The cotton wool will catch moisture, and from all this I think that the best foam would be sprayed. But this is only my summary
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  • #3 16952028
    chudy0321
    Level 9  
    no, but it is not known what the cost of such an operation and later wants to cover it from the inside OSB, you will have to equal the foam: /
  • #4 16952057
    barton21
    Level 26  
    So only steropian remains. The foam comes out about PLN 55 per m2 with 20cm insulation thickness
  • #5 16952069
    chudy0321
    Level 9  
    and what about insulation from the inside will be ok or not insulating from the inside /?
  • #6 16952077
    1repcaK
    Level 21  
    Warming up the unheated room I would wonder if the skin is worth the trip.
  • #7 16952091
    barton21
    Level 26  
    In general, I think that you can insulate from the inside. Only with steropian or foam. What you insulate depends on your wallet capacity really. You just have to calculate the costs and see what you get cheaper.
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  • #8 16952138
    chudy0321
    Level 9  
    I always count twice and check where cheaper materials are good, I am smarter for some knowledge, thanks for the information. Regards

    Added after 1 [hours] 15 [minutes]:

    1repcaK wrote:
    Warming up the unheated room I would wonder if the skin is worth the trip.



    but with time he wants to put a goat :)
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  • #9 16970954
    wnoto
    Level 34  
    And how will you insulate the roof? And how is he made? 44m2 is not a small garage ...
  • #10 16971051
    chudy0321
    Level 9  
    I have a membrane on the roof and the ceiling made of wooden boards is warmer like at the bottom
  • #11 16971228
    Anonymous
    Anonymous  
  • #12 16972385
    chudy0321
    Level 9  
    oki thank you so much for all the information
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Topic summary

✨ The discussion revolves around insulating a 44m2 unheated concrete slab garage. Users debate the merits of using wool insulation versus 5cm foam, with a consensus leaning towards foam (specifically steropian) due to its moisture resistance and cost-effectiveness. The cost of foam insulation is noted to be approximately PLN 55 per m2 for a thickness of 20cm. Concerns are raised about the effectiveness of insulating from the inside, especially for a garage that is only occasionally heated. Suggestions include considering the insulation of the roof and ensuring that the insulation is applied on the colder side. The importance of calculating costs and exploring cheaper materials is emphasized.
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FAQ

TL;DR: For a 44 m² unheated slab garage, users report spray foam at ~55 PLN/m² for 20 cm, and advise “only with styrofoam or foam.” [Elektroda, barton21, post #16952057]

Why it matters: This FAQ helps DIYers decide wool vs foam, plan OSB cladding, and avoid moisture pitfalls in intermittently heated garages.

Quick Facts

Is mineral wool a good idea for an unheated garage?

Forum users caution against wool inside an unheated garage because it can trap moisture. If you heat only occasionally, moisture cycling risks damp insulation and OSB swelling. EPS or spray foam behaves better in this scenario. “Better styrofoam.” [Elektroda, barton21, post #16952011]

Can I insulate a concrete-slab garage from the inside?

Yes. Contributors confirm interior insulation is workable for a free‑standing, seldom‑heated garage. They recommend EPS boards or spray foam, then cover with OSB for durability. Interior work is simpler and cheaper than exterior retrofits for small projects. [Elektroda, barton21, post #16952091]

What thickness or cost should I plan for spray foam?

A reported benchmark is about 55 PLN per m² for 20 cm thickness. Cost varies by region and contractor, but this gives a planning anchor. Use it to compare against EPS plus labor and OSB. [Elektroda, barton21, post #16952057]

Will I need to level spray foam before fixing OSB?

Yes, expect levelling or furring for a flat OSB finish. One user noted concern about evening foam before cladding. Plan furring strips or shave the foam to plane. [Elektroda, chudy0321, post #16952028]

What’s the simplest material stack for walls?

Typical sequence discussed: concrete wall, interior insulation (EPS or spray foam), then OSB sheathing. This balances cost, speed, and impact resistance for a hobby garage. Adhesive‑fixed EPS plus mechanical anchors works; spray foam bonds directly. [Elektroda, barton21, post #16952091]

How warm should I target for occasional work in winter?

A contributor suggests 14–16 °C as a practical goal for typical garage tasks. Short sessions in that band feel workable without heavy heating bills or over‑insulating. [Elektroda, 563113, post #16971228]

Does the roof/ceiling build affect my decision?

Yes. The OP’s roof has a membrane and timber ceiling boards. With that setup, adding OSB or similar to improve the ceiling lining can help comfort and reduce drafts while you insulate walls. [Elektroda, chudy0321, post #16971051]

Is it worth insulating if I only heat with a small stove (‘goat’)?

If you’ll add a small stove later, interior insulation plus OSB still helps reach workable temperatures faster. One user questioned payback in unheated spaces, but the OP plans a stove, which justifies basic insulation. [Elektroda, 1repcaK, post #16952077]

What’s an edge case where insulation fails?

Using mineral wool without airtight layers in a sporadically heated garage risks moisture absorption and degraded performance. That can also warp OSB. Choose EPS or spray foam to reduce moisture risks. [Elektroda, barton21, post #16952011]

Quick 3‑step: how do I insulate inside and finish with OSB?

  1. Fix EPS boards or apply spray foam to interior slabs.
  2. Create a flat plane with furring or foam trimming.
  3. Screw OSB to furring; seal joints.
    “Only with styrofoam or foam.” [Elektroda, barton21, post #16952091]

What is OSB, and why use it here?

OSB is oriented strand board, a strong wood panel. It protects insulation, takes screws for shelves, and resists impacts. Users plan OSB over interior insulation for a durable workshop finish. Seal edges against humidity. [Elektroda, chudy0321, post #16951992]

Should I prioritize insulating the roof or the walls?

A participant asked about roof plans first, highlighting its importance. If your roof has only a membrane and boards, improve that lining and then do walls to reduce heat loss and drafts. [Elektroda, wnoto, post #16970954]

How big is the example project this advice references?

The thread centers on a ~44 m² concrete‑slab garage. Use that scale when estimating material quantities and time. This statistic anchors budget comparisons. [Elektroda, chudy0321, post #16951992]

What do users recommend in one line?

“Only with styrofoam or foam.” This captures the forum consensus for inside insulation plus OSB in this use case. [Elektroda, barton21, post #16952091]

If I only sheath with OSB and skip insulation, is that acceptable?

One user suggested OSB alone might suffice if you heat only sporadically to 14–16 °C. It improves comfort slightly and tidies surfaces, but insulation improves heat‑up time. [Elektroda, 563113, post #16971228]
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