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Screeding and Insulating a Garage Floor

This is a guide on Screeding and Insulating a Garage Floor in the UK.  You are probably reading this because you are thinking of turning your garage into a liveable space. one that is warm in the winter and cool in the summer.  We all know that most people never use their garage to store a car, which is what garages are designed for.  Instead it is usually a convenient area to things like BBQ’s, lawnmowers, and random junk.  Converting your garage into a room such as a gym, kids playroom or office is a cost effective way of creating additional space.  We converted a customers stand alone garage into a bar

In general, garages are designed for storage space only, not living spaces.  This means your garage is probably not insulated, and therefore very cold, maybe even damp.  Screeding and insulating a garage floor to a height of 150mm is always the first step you should take when converting a garage into a living space.  Installing a Damp Proof Course (DPC), insulation and concrete will keep the moisture out, whilst helping to keep the heat in.

Reasons Why You Should Insulate a Garage Floor

Make your Converted Garage Warmer

You are probably aware heat rises, therefore most of your heat will escape through your garage walls and ceiling.  So why insulate a garage floor if heat rises? Well, an insulated floor does help to make your garage warmer.  This is because the insulation in the floor provides a thermal barrier between your garage and the outside environment.  A non-insulated garage floor wants to be the same temperature as the ground outside your garage.  Concrete also takes a very long time to warm up, and will feel very cold on your feet unless it is insulated.  Having insulation in your flooring will reflect heat back in the room through your floor, making your floor feel much warmer than a non-insulated one.

Help Prevent Damp

Your garage floor is designed to be level with the ground outside.  However, this allows water and debris to enter the garage occasionally.  If you are converting your garage, then you will need to raise the floor and create a Damp Proof Course (DPC).  You may have noticed your floor inside your home is higher than the ground outside, this is because your home has a damp proof course. A DPC is basically a water proof lining in your floor and external brick wall that prevents water in the ground entering your home. 

How to Screed and Insulate A Garage Floor

Step 1. Decide if you Need to Create a Doorway

If you are screeding and insulating your garage floor, then you are probably wanting to do this for two possible reasons.    

If making your Garage a Room within your Home:

If you are thinking of adding an additional room to your house by converting your garage, then you will first need to read the building regulations carefully.  This is because you will need to create a doorway or opening on the garage wall that is adjacent to the house.  The doorway opening to the garage will require a support such as a lintel.  Once this is done you will then need to remove your garage door and brick up the entrance.

If your garage will be seperate from your home:

If you are happy for you garage to be a stand-alone building, not directly connected to your home via a doorway.  Then you will need to think about the type of access door you want.  Either way, you will be required to remove your existing garage door.  This is because you need to build 2 brick layers (150mm high) from the ground where the garage door was.  This brick wall helps to contain the DPC and helps to prevent damp from rain water entering through the bricks.  You can then build a new front to your garage with its own uPVC or composite front door.  Or you could even put a window there and have a door the other side.  Whatever you do, make sure you research the regulations.

Step 2. Laying the Bricks

Follow this bricklaying guide to build 2 layers of bricks at the entrance of your garage.   The total height of your brick courses should be 150mm.  This will help contain the plastic DPC sheet, insulation and concrete.

Step 3. Ensure your Floor Surface is Clean

Make sure the surface of your floor is clean and free of debris. 

Step 4. Lay out DPC Sheet

Buy a decent DPC sheet, such as this Black Heavy duty DPC sheeting from Amazon. Then lay this onto your garage floor.  But make sure there is about 170mm going up the wall around the internal perimeter of your garage. Ideally you need 1 piece of sheet to span the length and width inside your garage, with all edges going up the wall about 170mm. Think of this DPC sheet as a container for the concrete you will pour later.   

Step 5. Laying Down the Insulation

Buy 100mm of rigid foam insulation , such as this Celotex insulation from Amazon.  Fill the entire space of your garage floor with this insulation, then tape together using lagging tape.  Please do not use aluminium foil tap, as this could react with the cement. The image shows the black DPC laid down, with the celotex foam insulation pushed against the walls. Notice how the DPC also goes up the wall. You would need the entire floor covered in 100mm insulation. 

screeding and insulating a garage floor

Step 6. Pouring the Concrete

Follow this guide to mixing concrete. Then pour the concrete over the insulation so that the voids are filled.   Pour to a total height of 150mm.  Make sure you pour the concrete uniformly, so you fill the garage floor at the same rate.  Let your concrete floor dry for 1 week before walking on it. Below is an example of a insulated garage floor, filled to a height of 150mm. You will notice that some of the DPC sheet is showing around the perimeter.

Step 7. Install a Front or Back Door

You will need to select a suitable door for your converted garage. Or maybe you do not need one if you are knocking through to your home. Below is an image of a composite door we installed for a customer’s garage that we converted into a bar. We constructed walls to create a door opening at the front. Then screwed a composite door into those walls, and into the 2 brick layers that were built for the DPC.

Posted on 19th January 2021 at 7:18 pm

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