Converting an underused garage into everyday living space is a simple and effective way to add square footage to your home. It's much less expensive than adding and adds breathing room to a growing family's nest. Since the floor of a garage is typically 20 cm (8 inches) lower than the rest of the house, you may want to raise the floor.
- Converting an underused garage into everyday living space is a simple and effective way to add square footage to your home.
- Since the floor of a garage is typically 20 cm (8 inches) lower than the rest of the house, you may want to raise the floor.
Check with your local city or county for building codes in your area. Measure the room's height from the house level up to the rafters to make certain the clearance is within the building standards.
You may need to add trusses since garage trusses can be set 60 cm (24 inches) apart, but trusses over living space must be 32.5 cm (16 inches). If you need to create more headspace, consider a cathedral ceiling if the garage can accommodate one or have one step down into the room.
Clean out the garage and sweep the floor free of all debris.
Mark a line around the garage to show where the house level is. Garage floors often slope, so don't measure from the floor up, but rather from the house line down. Leave room for a 1.8 cm (3/4 inch) plywood subfloor, plus the thickness of the flooring installed when determining how high your decking should be.
- Clean out the garage and sweep the floor free of all debris.
- Mark a line around the garage to show where the house level is.
Lay down a protective barrier of polythene sheeting. Overlap the sheets by several inches and tape them with masking tape to ensure a waterproof barrier. Affix the sheets to the garage perimeter with masonry nails. Apply caulk to the edges to seal, using a caulk gun.
Build a frame from pressure-treated lumber to the height you have determined. Place the studs 32.5 cm (16 inches) apart. Add shims to maintain a level floor throughout, as necessary. Check level constantly during this process. Tie the frame into the walls with masonry nails.
Add insulation between the studs, as well as any plumbing pipes or electrical wires needed.
Lay 1.8 cm (3/4 inch) plywood on top of the stud frame, running the plywood sheets across the studs. Nail into the studs with 3.7 cm (1 1/2 inch) wood nails.
- Build a frame from pressure-treated lumber to the height you have determined.
- Lay 1.8 cm (3/4 inch) plywood on top of the stud frame, running the plywood sheets across the studs.
Finish the floor with your choice of carpet, tile or wood.
One thing to remember is the regulation regarding a ‘fire step’ down into a garage from a habitable room. Once your conversion becomes a habitable room, this regulation is no longer needed. If, however, you intend to divide your garage up into habitable space and a car parking space, you will need a 4” step down into the garage area.
It’s highly unlikely the existing garage floor will contain an insulating material, in which case you’ll need to introduce it to some sheet insulation. You could go for a ‘floating floor’ or a sand/cement screed finish, sometimes depending on the depth you have to play with.
If the access door to the garage is near the back, then the floor will likely be near its highest point. A sloping concrete finish is usually incorporated into garages to prevent puddles and wash from wet weather, which means the door will be the lowest.
If, however, the garage is a built-in design and relatively modern, it may well already be insulated and will require little or no extra. However, if you cannot prove the existence of insulation to the building inspector, you may have to dig a test hole to do so, or it may well be easier to go ahead and insulate it anyway, saving the hassle.
When screeding the floor, you’ll need a minimum thickness of insulation followed by a minimum screed thickness. Reinforced screed (added fibres) is best. The step down into the garage from the finished floor level in the access door will give you a fixed height to work in an extension type conversion, whereas a detached version will give you some room to play with.
Floor screeding comes under ‘plastering’ and is essentially a 5:1 sharp sand: cement mix, just moist, not wet and laid to a depth of 50-75mm with a float finish (smooth and flat) you can finish per normal. It’s a skilled trade similar to plastering, so it pays to have a professional rather than try and do it yourself if you’ve never done it before.
A DIYer working from written instructions for the first time is likely to make a mess of it and waste the price of the materials. The insulation you install will depend on your step down height but will need to at least achieve the required ‘u’ value. In 2009 50mm of Celotex under 50mm of reinforced screed was sufficient.
Floating floors consist of sheet insulation under a layer of solid floorings such as chipboard tongue and grooved 8 x 2 sheets. The problem here is the existing slope of the floor. An exterior grade levelling compound will level the floor before installing the uniform sheeting.
Getting the existing floor perfectly level will result in a perfectly level floating floor. There's also nothing to stop you from increasing the insulation to make up height or even doubling up the chipboard flooring. There's also nothing to stop you from finishing for the last millimetre with a flexible floor levelling compound.
Celotex is usually available in multiples of 25mm thickness and chipboard flooring in 18mm or 22mm. It pays to get the water-resistant type. Non-water-resistant will be cheaper by about a pound a sheet, and you only need ten sheets per garage, so the extra tenner is worth it.
A downside to installing a floating floor is if there is a water leak, it can remain undetected for some time as the water can immediately run over the edge of the board down into the insulation and build up until what you're left with is a real genuine ‘floating’ floor. It will rot any timber over some time, treated or not. A screed floor will dry out. Floating floors need replacing…
Wondering how to raise the garage floor for living space? Before you get started, check for these three important project elements.
Building Regulations: Flooring
The existing garage floor is likely to be strong enough for general domestic use but may need to be upgraded to ensure it is adequate in terms of damp-proofing and thermal insulation. It may also be desirable to change the floor level to match the levels in the existing home.
The simplest way to achieve this would be to upgrade the existing concrete floor. Alternatively, if levels permit, a new timber floor could be constructed over the existing concrete floor.
Solid floor
The existing concrete floor can be used as a base. However, a new damp proof membrane (DPM) will need to be introduced. DPMs come in solid or liquid form, a viable solution for a garage conversion. Manufacturers will be able to advise. A suitable gauge damp proof membrane (DPM) and thermal insulation must be provided. These can be laid over the sand blinding or on the concrete.
Thermal insulation may be required and can be placed on top of the membrane (if a liquid membrane is used, care should be taken to ensure the two materials do not react - a separation layer may be needed). The exact details will vary depending on which products are used.
The floor can be finished with a screed layer or a timber covering ("floating floor"). The exact specification will depend on the insulation material used beneath. A screed is likely to need to be 75mm thick and should include a reinforcement mesh to prevent it from cracking.
Care should be taken to ensure any existing air bricks for the main house are not obstructed by this work. They should be extended through the new floor to external air.
Suspended Timber Floor
The current floor level of the house may be quite high above the ground, and in cases such as this, it is more practicable to use timber joists with a void underneath. A minimum gap of 150mm should be kept between the existing concrete ground and the underside of the timber. The timber floor joists must be sized correctly depending on their length. They are then laid across the shortest span from wall to wall with a gap underneath.
An intermediate wall with a small footing may be needed to reduce the span and keep the thickness of the floor joists to a minimum. A damp proof course (DPC) should be placed on the underside of the timber.
Insulation is then placed between the joists (thickness required depends on the product used). Air vents should be placed underneath to provide ventilation to the void, and the air should be able to travel from one side of the building to the other.
How to Raise Floor Height in Your Garage: Getting Started
Adding living space to an existing house can be an expensive project, often requiring on a smaller scale the same construction techniques as those used within the house itself. A less expensive alternative is to convert an attached garage instead.
Unfortunately, your garage floor may not be level with the floor of your household, creating a possible tripping hazard. You can correct this issue by raising the garage floor to meet your house.
By using a permanent concrete overlay consisting of the self-levelling compound, you can create solid concrete surface inches above the original garage floor, ready for covering however you wish.
Check the building codes and local zoning laws to see if this is permissible.
There may be restrictions on a height that may be a qualifying factor, as generally, garages are built of a height not more than 8 feet. So if you raise the floor, you have to check the minimum height available after raising the floor.
Ensure this is within the building codes. If it is not, see if you are inconvenienced by creating a step between the house and the garage area.
Measure everything!
While measuring these heights, use a level to mark a common datum on the garage walls and base all your measurements on the house floor, the garage floor, and the roof. Quite often, garage floors will be sloped, and this requires you to be more circumspect.
If you think you need to put in a few windows for light, do these works before you do the floor raising, again keeping the sill per the raised floor.
You would also need to decide how you intend to close the garage door. You can always replace it with an external wall, but using drywall inside the door to match the surface to the existing walls could be a solution.
Check the dampness on the garage floor.
Garage floors are normally of almost the same level as driveways, and there is every chance the dampness from surrounding areas could get into your garage. If there is a dampness problem, tackle this first with poly or other liners.
- Step 1: Clear the garage floor of everything and then clean the floor thoroughly. Clean out any cracks with a wire brush and remove loose concrete chips by chipping away the loose concrete with a cold chisel and hammer. Sweep the floor using a stiff-bristled broom to remove all loose dirt and debris. Use a concrete degreaser to remove any oil spills. Wash the floor with a pH-neutral cleaner, and then rinse the surface with clean water. Wait for the concrete to dry before continuing.
- Step 2: Repair the garage floor using joint repair compound and mortar. Fill any cracks in the floor with a joint repair compound. Press the compound firmly into the cracks with a putty knife and then scrape the surface of the patch with the knife-edge to level the surface of the crack. Fill dips or spalled concrete areas -- where chunks of concrete separate from the surface -- with mortar. Brush the sides and base of the damaged area with epoxy adhesive. Use a trowel to apply the mortar to the damaged area, levelling the patch with the surrounding concrete. Allow the patches to dry overnight to begin setting.
- Step 3: Remove all baseboards or trim surrounding the garage floor. Pry the boards away from the walls using a pry bar, and then place the boards aside for reuse after adjusting the floor level.
- Step 4: Open the garage door and attach a board at the edge of the floor where the door usually rests. Secure the board in place by nailing it to the garage walls. Use a board that's as high as the newly intended floor level. Place a bead of silicone caulk at the board's base in the garage interior to prevent the self-leveller from seeping beneath the board.
- Step 5: Cover the garage floor with a thin epoxy adhesive layer. Brush the adhesive over the floor to act as a bonding agent for the new floor material and the existing garage floor. Allow the adhesive to dry until it loses the wet look while remaining sticky to the touch.
- Step 6: Mix a batch of the self-levelling compound in a large bucket using an electric drill with a paddle bit. Follow the manufacturer's instructions when mixing the leveller material, but use cold water to slow down the curing process slightly to extend the time you have to work the material.
- Step 7: Pour the compound over the garage floor, using a squeegee to spread the material. Spread a layer up to two inches thick, and then wait four hours for the compound to set. It will level itself as it settles, creating an even finish.
- Step 8: Continue to pour the compound in 2-inch layers until you reach the level of the house floor. Allow the same four-hour setting time between each 2-inch level, but allow 48 hours setting time after spreading the final layer for complete curing of the levelling compound. Most compounds can support up to three 2-inch layers as long as they have aggregate included, while others are limited only by the support of your subfloor. Check with the manufacturer the thickness achievable by the specific material in use.
- Step 9: Remove the board blocking the garage entrance and lower the garage door. Replace the baseboards if desired by nailing them back into place.
FAQs About Garage Renovation
Building codes are used to stipulate that the floor of an attached garage be four inches lower than the floor level of the house. The rationale for requiring this little step was to prevent spilled gasoline, gasoline vapours, and carbon monoxide from getting inside the house.
For example, the garage floor is typically made on the same level as the rest of the house because it was intended to be an optional garage conversion, which means it isn't intended to be occupied by vehicles.
4 inches.
The recommended thickness for a car lift concrete slab is 4 inches minimum for most two-post lifts and four-post lifts.
Ideally, make the floor slope slightly from the back to the front so any water or snowmelt brought into the garage will drain out.
The best solution to fixing garage floor settlement is through concrete lifting. By drilling small holes in your floor and pumping in organic or foam material to stabilize the soil, the slab is lifted and made level once again.
Conclusion
Normally, garage floors are about 8 inches below the general house level. This height can be easily made up with a layer of insulation and some concrete screed. This will leave you a sufficient margin for the final floor tiles or another flooring that you propose for your new living space.
Raising the garage floor is the easiest and fastest way for a DIY project. But if you are planning to have a lot of electrical points or other wirings in the new space, it may require a lot of detailed planning before you lay down the concrete. By the way, insulation is suggested to keep the temperature in the modified space uniform.