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Converting an integral garage into an office

Postby ShaneCook » Mon Jan 26, 2009 11:19 pm


I started converting my garage into a small office area and then realized that an office counted as a habitable room so I required building regulations approval, which I've just started reading about.

Now I could have stuck my pc in my drafty old integral garage, but that would have been very cold, so I decided to make the place a little warmer. I'm guessing I did a few things right and a few things wrong. I'd like to apply for building regulations so if someone could point out where I went wrong that would be very helpful.

The garage is an integral one. It has a wooden garage door at one end, a concrete floor, fireproof plasterboard on the wall to the house and the ceiling. Breeze blocks on the outer wall, with that yellow itchy insulation in the cavity to the outer brick wall.

1. First of all I bought a DPC sheet and put in on the concrete floor, not that there was every any damp, but because I knew you were supposed to do this.

2. Then I put 50mm of polystyrene on the floor so it came up to the edges of the walls, but pulled the DPC up around, so the DPC sat between the polystyrene and the wall.

3. I then put 18mm tongue and groove chip board, with a 10mm gap to the wall either side.

4. As the floor was too low, I repeated this and put another 50mm of polystyrene and another 18mm of tongue and grove flooring. The floor height is now correct and will give me enough room for the foam underlay and laminate flooring.

5. Next I built a stud wall about 100mm behind the existing garage door using 50mm x 25mm timber. I filled the gaps between the wood with 50mm polystyrene and taped around each join to stop any draft blowing through. The bottom of the stud wall sits on the wooden flooring and the DPC was brought under and around behind the stud wall and cut 100mm or so above the bottom of the wall.

5. I then put plasterboard over the wooden frame and sealed the edges with mastic so no drafts came in.

6. For the internal breeze block wall I bought some 68mm x 25mms studs and intend to make a frame, fixed to the blocks using those hammer in masonry bolts, where you drill a pilot hole and then hammer in the last part. I was then planning to put some more 50mm polystyrene and cover it with plasterboard, thus making every wall plastered boarded.

7. Winter was the providing ground and it got too cold in the garage, and in particular, drafty around the garage door. I therefore got some expanding foam and sealing around all four edges of the door to stop the wind blowing in and that helped a lot, as did sealing all the holes around the existing window frame with mastic. I also sealed any holes I could find where the masonry was done poorly and wind was come in.

I was planning on adding a radiator off the central heating when I get the heating people to change my old boiler, and then having the room plastered before putting down the wooden flooring. The old garage already had lighting and electric.

A few things I did wrong (please add some more):

A. Not putting insulation directly behind the garage door, or sealing it with expanding foam from the inside (much easier). However, as I plan to open up a second of the plasterboard behind it to access open up the small roof space, I have the option of putting something down from the roof into the void. I was thinking of those tiny balls maybe that packing insulation. I can also then insulate the garage roof, which has only 25mm to 50mm over the plasterboard and none on the sloping roof section.

B. Not realising I needed building regs, so now I need someone to draw up some plans and will apply retrospectively.

C. Not knowing you could get plasterboard with insulation on the back.

D. I don't know even today, how much extra insulation is worth adding to the breeze block walls. The house was built in 1989.
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Postby thedoctor » Tue Jan 27, 2009 7:56 am

There is s short checklist for Garage Conversions in the DIY Projects page. Take a look at that to get the basics then at the building regulations projects where everything is covered
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