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I'm considering installing drywall in my attic, which has a sloped ceiling. Some suggest starting by placing studs (ceiling joists) along the same line as the current ones (behind the vapor barrier), followed by adding additional studs at intervals of 25cm in a standard orientation. This arrangement is depicted by the red and green lines in my photos, respectively. Alternatively, others recommend solely installing the green studs (refer to the photo). What would be better? Also is using metal better than wooden studs?

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    Just a comment because I'm really out of my league here: 1 - 25cm ~= 10" - normal spacing is 16" or 24"; 2 - metal and wood each have advantages, but if you already have wood I would stick with wood (puns intended) so that you can stick with one type of drywall fastener, etc. Plus metal conducts heat much faster than wood so I would think (but others may tell me I'm wrong) that wood would work better for that reason.
    – manassehkatz-Moving 2 Codidact
    Commented May 10 at 15:03
  • What is the ventilation and insulation in the ceiling? Closing up that space with drywall has potential repercussions. (And as a pedantic aside, let's please call rafters rafters and sticks running sideways across the rafters, "cross strapping". Studs are uprights that make up a wall.)
    – Aloysius Defenestrate
    Commented May 10 at 15:38
  • @AloysiusDefenestrate - I have never heard of non-structural framing referred to as strapping or cross strapping.
    – DMoore
    Commented May 10 at 15:50
  • @DMoore -- there's always regional variance. What would a 1x4 run perpendicular to framing on the ceiling be called in your neck of the woods?
    – Aloysius Defenestrate
    Commented May 10 at 15:55

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If the attic ventilation, insulation and vapor barrier are all done within the rafter spacing, and the rafter-to-rafter spacing is 24" (60.96cm) or less, screw the drywall into the rafters and call it a day.

The only reason to add to the rafters would be if you needed to add more insulation. And in that case using rigid foam insulation sheets over the rafters before the drywall (screwed into the rafters with longer drywall screws) is more effective than adding lumber to the rafters and batts between them.

Putting strapping (nominal 1x3 or 1x4 lumber) perpendicular to the rafters on 12"/30.48cm spacing will provide more support to the drywall, but that is usually only needed if the drywall is holding up a large amount of loose fill insulation, which gets heavy. If the insulation is not loading the drywall, direct attachment to the rafters wastes less interior space. 25cm spacing is odd, and it won't line up with the edges of sheets which are 48" (121.92 cm) wide.

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  • My intuition is that rafters are at 19.2”, so 3 per 48” space. Not great for holding up rock, imho.
    – Aloysius Defenestrate
    Commented May 12 at 14:01
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    USG (a major manufacturer of drywall panels) states that 24" on center is sufficient unless you are using 3/8" rock or applying it parallel to the framing rather than perpendicular. See page 7 usg.com/content/dam/USG_Marketing_Communications/united_states/…
    – Ecnerwal
    Commented May 13 at 2:21
  • Appreciate the reference, @ecnerwal — one would just want to make sure all the screws are perfect.
    – Aloysius Defenestrate
    Commented May 13 at 3:32

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