I am in the process of utilising the rear half of my detached garage for a hobby room. We have a pitched roof, so joists are 600mm centres.

I have read a few previous question/answers...I take it that using the 12.5mm fire resistant board for the ceiling and dividing wall is worth it for a number of reasons.

In terms of the dividing wall, what is the better option for timber? 50 x 75 or 50 x 100?

Also, do I need to have a 'step' in the door way to cover regs?

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    – BMitch
    Commented Jan 4, 2020 at 0:32
  • Reading this wonder what country Paul is from. Does ICC apply. Millimeter could mean Europe.
    – Ride Sun
    Commented Jan 4, 2020 at 1:37
  • You should get some real advice from someone on your side of the pond. I have received 84k is dollars after purchasing a large house that had 5 bedrooms and 3 baths ,,, turns out only the 2 baths and 2 bedrooms on the main floor were legal living spaces , a detached garage, NOT a living space unless WAY More than a wall . So go ahead and build it and try to sell it and end up in court and loose anything you thought you had. I tried to have the seller make adjustments he went to court and lost the house ended up costing me 18k , I raised the main floor 16” and sold it 2 years later for 3x.
    – Ed Beal
    Commented Jan 4, 2020 at 21:43
  • I'm in the UK. A surveyor would surely point out any issues prior to selling, so i would expect any problem to be rectifiable. I'm only putting dividing wall up, so nothing is permanent if it needed changing/removing
    – Paul
    Commented Jan 5, 2020 at 14:46

2 Answers 2


A hobby room is considered a “living space” and a “habitable room” on this side of the pond and probably on your side of the pond too, because the code is written by the International Code Council (ICC). (See ICC R202 Definitions)

Likewise, Garages are to be separated from single family residences by 1/2” gypsum board on garage side ONLY, provided the garage does not open into a sleeping room. (See 2017 edition ICC Table R302.6.) It DOES NOT matter if it’s a bearing wall or not.

Also the door between the garage and house shall be a solid wood door a minimum of 1 3/8” thick and is not permitted into a sleeping room. (See ICC R302.5.1.1.)

In order for the 1/2” gypsum board to be allowed and effective, it must be nailed into a minimum of 1 1/2” thick x 3 1/2” material at 16” on center. (5/8” thick gypsum board can be nailed at 24” on centers.)

Side note: You are creating a “fire wall” between the garage and living spaces. Usually gypsum board is required on both sides of the wall, but in this case, the “hazard” is located in the garage.

Oh, BTW, it’s not required on the ceiling of the garage unless there is a habitable room above.

AND no step is required at the doorway. In fact, the inside cannot be more than 1 1/2” difference than the outside, unless the door does not swing out over the landing then it can be 8”, or if it’s a handicap accessible route...in which case the maximum difference is 1/2”. (See ICC R311.3.1)

  • Thanks. As mentioned in the question, the garage is 'detached' from the house, so I take it some of that does not apply?
    – Paul
    Commented Jan 2, 2020 at 20:35
  • 1
    Just putting a wall in a detached garage so not a living space! I would question if the height alone would be classified as the doorway is at the roof line.
    – Ed Beal
    Commented Jan 3, 2020 at 16:27
  • @EdBeal The OP said they intend to use the new space as a “hobby room”.
    – Lee Sam
    Commented Jan 3, 2020 at 16:30
  • i See lots of basements with 6’6” ceilings these are not legal living spaces so it doesn’t matter what you call it.
    – Ed Beal
    Commented Jan 3, 2020 at 16:33
  • @EdBeal I don’t understand your basement statement. Are you saying that if a room is not “legal” then you can call it anything you want?
    – Lee Sam
    Commented Jan 3, 2020 at 16:40

Your code may be different but on this side of the pond the thinner lumber would be ok as it is not a load bearing wall. A hobby room also is not a living space so it may not require fire resistant wall board. I would check with the local building code enforcement to make sure I was doing it to code.

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