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
- Area discussed: ~44 m² concrete-slab, unheated garage. [Elektroda, chudy0321, post #16951992]
- Reported spray foam cost: ~55 PLN/m² at 20 cm thickness. [Elektroda, barton21, post #16952057]
- Forum consensus: inside insulation is acceptable; choose styrofoam (EPS) or spray foam. [Elektroda, barton21, post #16952091]
- Roof noted: membrane over boards; ceiling is timber sheathing. [Elektroda, chudy0321, post #16971051]
- Practical work comfort: 14–16 °C is sufficient for garage tasks. [Elektroda, 563113, post #16971228]
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?
- Fix EPS boards or apply spray foam to interior slabs.
- Create a flat plane with furring or foam trimming.
- 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]
