Garage conversion floor insulation needs to be considered as part of the complete floor and its connection to the house. The insulation board alone does not establish the finished level, damp protection, threshold detail or usable room height.
Start with a survey of the existing construction and levels. Ask the designer and relevant trades to agree the proposed build-up before doors, fitted furniture or final floor finishes are ordered.
Record what is there before choosing a build-up
Measure the relevant existing and adjoining floor levels and identify what is known about the garage slab and its condition. Record visible damp concerns and areas needing investigation. Do not assume an existing concrete floor is suitable just because it looks solid.
The Planning Portal's garage flooring guidance discusses damp protection, insulation and the effect of levels, while noting that product choices affect the details. Use the appointed designer’s assessment for your construction, and do not adopt a generic build-up.
Compare the complete assembly
Ask for the proposed layers and their functions, including the finish. Identify who checks compatibility and what information is needed for the applicable building-control process.
| Item | Question for the project team |
|---|---|
| Existing floor | What construction and condition have been verified, and what remains unknown? |
| Moisture protection | Which specified arrangement is proposed and how does it meet adjacent construction? |
| Insulation | Which product and design requirement apply to this complete floor? |
| Support and finish | What carries the chosen finish and what preparation does it need? |
| Levels | Where will the finished surface sit relative to the house, doors and external thresholds? |
| Interfaces | How are services, existing ventilation and future access dealt with? |
This original level-and-build-up worksheet is for briefing the designer and installer. It is not a structural assessment or a specification for an unknown slab.
Check the connection to the house
A continuous-looking floor finish can still cross different construction. Ask how the threshold and junction are being detailed and which levels are fixed by the adjoining room.
Mark the bottom of door openings and any service route that affects the proposed depth. Check the resulting room height and the interfaces with wall construction, insulation and fitted elements. Keep existing ventilation requirements in the design discussion.
An example of why the finish choice matters
Say the proposed garage room is being coordinated with one floor finish and the owner later chooses a different assembly. This is a hypothetical planning example. The team needs to revisit the complete thickness and readiness requirements before assuming that the original threshold and door details remain suitable.
Record the updated product, drawing revision and decision. The change may need coordination with other work even when the insulation product itself has not changed.
Define the quotation boundary
List investigation, removal, preparation, moisture protection, insulation, the specified floor construction and the finish separately. Identify client purchases, work by others and the checks or documents expected at handover.
Keep any unknown condition visible. Agree how additional work would be assessed and instructed if investigation reveals a different background from the one assumed.
What to send with a garage enquiry
Send the London postcode, photographs, existing and proposed layout, known floor levels and any design or survey information. Tell us the intended room use and your finish preferences. We can discuss the garage conversion package and the information needed before the floor construction and quotation are settled.