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I have a cold attic meaning the insulation is on the bottom. I would like to put flooring here so that I can use this area as storage without abusing it.

What do I need to pay attention for this job?

  • There is already some kind of (a bit worn out) protection wrapping the insulation. Do I need to put anything else?
  • I prefer screws over nails just because it is faster. Is it the right choice or can screws snap off over time if the house is moving slightly?
  • Do I need to leave any space between the timber pieces in case they expand?

Right now it is winter in Sweden and this is how my attic looks!

enter image description here

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    Any wiring on top will need to be protected, the space doesn't look that wide so the addition of decking and light storage loads will probably be fine. Screws will be better for the install because pounding above Sheetrock can cause cracks. If there are electrical boxes for lighting I usually try to keep these accessible in case future additional fixtures are desired. – Ed Beal Feb 10 '17 at 16:15
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First thing, I'll check the ceiling joists. In US/Canada it's not uncommon to use joists sized and spaced to only support the ceiling drywall below, e.g. they are not sized to support any kind of storage or any other regular activity in the attic. I'm not sure about laws and practices in Sweden, though.

Now, to actually answer your question: screws are perfectly fine. I'd just use a quarter or a similar coin to space timbers to allow for seasonal expansion/contraction. Unless you already have the timbers, I'd rather use strips of plywood or OSB, they are cheaper and do the job just as well. Just make sure they are small enough to be brought up into your attic.

  • Thank you very much for your time haimg. How can I check the ceiling joists? Is there anything I need to pay attention? – Umut Feb 13 '17 at 7:50
  • Measure the size of the joists (pull an insulation in one place a bit to measure them), spacing (between joists), and span (lengh of the joists). There are lots of online calculators and tables for joists sizing. Personally, I would be comfortable with 2"x6" joists for some light storage usage, if I feel no deflection when I walk up there (on the joists). – haimg Feb 13 '17 at 13:28
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Do I need to cover the insulation?
If there's a vapor barrier installed it'll be on the warm side. You can simply install flooring with nothing else over the insulation. I'd probably install a vertical board near the edges of the space to prevent items from falling off the floor and to prevent contact with the insulation.

Are screws appropriate?
Sure. Whatever is convenient. As this isn't a living space, squeaks from foot traffic aren't a real concern.

Do I need to leave any space between the timber pieces in case they expand?
I assume you're referring to the floor joists. No. What you may need to allow is a gap between your flooring boards, depending on what you use. Extreme heat in the summer could cause buckling. Follow manufacturer recommendations.

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If you're not sure on the spacing between joists, what I would do is run some 2x4s perpendicular to the joists and then use something like 3 inch (about 8cm) screws to attach them to the joists. For the cost and hassle, you get a few benefits

  1. You don't have to fiddle with wiring that's running across the joists. The wires can sit between the 2x4s. Avoids having to notch boards and still have visible wires
  2. It's better structurally. The 2x4s pick up the load and distribute it better across the joists. This means you can get some heaver things on the deck than a mere board would support.
  3. Easier to cut your boards (or potentially remove the need for cutting at all) to fit on the 2x4s. Sometimes you can find pre-cut boards (in the US they sell 2ft x 4ft pre-cut OSB that's 5/8" thick) and if you're making your own gaps you can plan to put the 2x4s to fit perfectly under the decking

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