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I have the following problem: my attic is mostly a crawlspace for the air-conditioning unit. And that crawlspace is full of obstacles, which makes my filter very hard to reach.

My solution is to make a second push-up hatch (or ladder hatch) that is right next to the filter, as opposed to the other side of the attic.

It would go here (view from crawl-space, looking down onto ceiling of top floor.)

enter image description here

Some googling makes me believe that I need to place a box, with Styrofoam lid in my ceiling. Also, that is what resembles my existing hatch, at the other side of the attic.

I've measured the beams (joists?) to be close together, with only a 39cm gap between them. I guess enough for a small hatch, of custom size?

enter image description here

Would I place my custom box on top of the timbers, or between the timbers? It looks like I need to re-route some electricity if it goes between the timbers.

There seems to be a plastic foil on the boards. Any concerns when I cut through that to create a hole?

For the hole, I guess drill 4 times, and with a reciprocating saw cut out the panel?

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You can use the existing door as an example.

A few things to pay attention to:

  • Your hatch must be special kind that is air tight when closed. If it's insulated (styrofoam) it's a bonus. You don't need an external hatch door. The airtight fit ensures that no warm and moist air from the house mixes with cold air in the attic to form condensation and related mold problems at the hatch. That's also what the purpose of the existing vapour barrier is, the plastic foil you mention.
  • The existing vapour barrier must form a closed seal with the door's trim: it is glued or taped or compressed with a foam lip. Your hardware store can show you which sealing method is best for the hatch you chose. The tape and/or glue are special for vapour seals, so make sure you get the right kind.

To cut the opening you need a drywall saw. No need to drill corners first. The saw has a pointy tip to help initial protrusion. They are cheap manual things and easy to use but messy.

You will use your hatch as the cutting template. Your hatch will likely be fitted from the attic side, protruding down, with the vapour barrier lip pressing against the vapour barrier foil and drywall. Then a trim is applied to sandwich the drywall and rim, and provide a finished look. The trim also conceals the drywall edge at your cut.

For best strength, you may need to build a small a wooden frame to the back of the ceiling drywall. This relieves mechanical stresses from repeated opening and closing and prevents cracking of the drywall. The frame is then attached to both joists. One side of the hatch, usually the hinge side, is screwed into one of the joists. The other 3 sides are screwed into the trim or rim of the hatch. For the frame you'll need 2x2 or 2x3 lumber. You will also screw the ceiling drywall into the frame you built. No need to mud the screw heads if the hatch has a trim that conceals it. So make sure that the frame is positioned tightly behind the trim.

If the door is smaller than 15in you do not need to move the electrical wire. However, make sure that while you are working on the hatch and frame that you do not squeeze/pinch the wire or screw/nail into it. You could move the wire a few inches further up the joist.

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  • I would recommend moving one joist bay to the side to avoid the wiring located in this bay. All in all, it would make the job easier and safer with nearly zero chance of damaging the wiring. Skinned cable should, technically, be replaced as the white cable housing is part of the protective insulation should there be a short in the wiring. If this ends up moving the new hatch too far away to reach the filter from the hatch directly, a piece of plywood/OSB can be laid across the joist bay toward the filter to make a handy platform to lean on while making the filter change.
    – FreeMan
    Apr 29, 2021 at 11:18
  • @FreeMan good idea. Another option with the wire is to protect it with a piece of 1x4 over the 3 or 4 feet length around the working area as a cover, and offset the protection from the joist with a spacer (1/2inch) or a cutting from the 1x4 (which is 3/4in thick) to provide a stable mount for the cover that does not compress the wire. Let's see what questions OP comes back with.
    – P2000
    Apr 29, 2021 at 14:18
  • @p2000 Thanks for the warning about vapor. I would have screwed that up. I cannot move to the side, there are large obstructions everywhere, like cold air tunnels from aircon, lines with coolant, etc. that narrow spot is my only option, and I am starting to think it is hopeless... 15” wont fit my shoulders. Existing hatch is much larger, but so far away, blocked by obstacles.
    – Bram
    Apr 29, 2021 at 16:26
  • @Bram there are also rectangular hatches that might fit you. There are companies specialized in this where you order directly, if not available at the hardware store. Or you can perhaps ask a local carpenter to build one for you. It doesn't really need hinges, but it does need some sort of lock to press and seal the panel against the jamb. PS I sent you a linkedin invite.
    – P2000
    Apr 29, 2021 at 16:42

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