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We have a loft room that is boarded and has insulated plasterboard attached to the rafters. There is a small gap between the bottom of the plasterboard and the flooring which I assume is compromising the insulation. I understand it is important not to block the space behind the plasterboard as this is needed to ventilate from the eaves, so I am reluctant to use expanding foam to fill this. What do people recommend?

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    A picture of the area will help. What needs to be done to correct will depend on the size of the "small gap" I assume this is an "A" frame type of situation and base or skirting board is not a feasible option.
    – RMDman
    Nov 27, 2022 at 22:53
  • Yes that’s right. Nov 28, 2022 at 7:06
  • It’s about an inch wide or so. I can stick my fingers through Nov 28, 2022 at 7:13
  • Added photo as requested. Nov 28, 2022 at 17:42
  • There's almost always a gap below drywall. It's not part of the building envelop and doesn't need to be sealed in any way. Please revise your post to explain the insulation and vapor barrier strategy employed behind the drywall. Proper answers depend on that information.
    – isherwood
    Nov 28, 2022 at 18:02

2 Answers 2

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That is normal, the gap helps prevent spills on the floor from soaking into the drywall.

To close the gap install a baseboard,

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The best course of action would be to remove the plasterboard (as it seems to be improperly installed, horizontal, and unfinished) and tightly insulate atop the studs and therefore behind the plasterboard. Large sheet/panel Styrofoam is the best very long-term option.

However, if you're mostly concerned about aesthetics, then just a tightly fitted and caulked baseboard would fit the bill perfectly.

Eave ventilation is only important with a proper path to Gable Vents, behind the walls, or to a Ridge-Vent system with a proper path behind the ceiling only.

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    There's nothing improper about horizontal drywall. Around here it's all installed horizontally, saving garage firewalls where taping isn't planned.
    – isherwood
    Nov 28, 2022 at 18:01
  • Because everyone else does it, doesn't mean it's right. 4-clicks down the scroll bar here diy.stackexchange.com/questions/28484/… will certainly get you started in understanding that there's nothing but wrong with horizontal.
    – Iggy
    Nov 28, 2022 at 18:12
  • The plasterboard is insulated plasterboard, so there’s already insulation on the roof. The house is mid-terrace and I don’t believe there are gable vents across the block but there is ventilation at front and rear soffits. The latter is close to the gap and what I want to make sure not to block. Nov 28, 2022 at 21:47
  • I’m not concerned about aesthetics. It’s a storage room within roof. What I’m worried about is cold air from the soffit vents entering the room. A skirting board would be possible, though awkward given the angle. I also wondered if it wouldn’t be a weak point in the envelope. Nov 28, 2022 at 21:49
  • Then you'll be in good shape in just filling the gap and even covering it. A squirt of Big Gap Spray Foam on the back of baseboard as it's applied will squish nicely. Leaving the gap though, can introduce too much humidity and heat to cause condensation or ice dams in cold winter climates.
    – Iggy
    Nov 28, 2022 at 21:55

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