Installing attic insulation

How do you install insulation in your attic? It is actually quite easy – and it will keep your home more comfortable all year round and will save you a lot of money. Last year’s winter here in New England was much colder than normal – enough to tack on an additional $1,000 to our heating bill. So I decided it was finally time to bite the bullet and add some more insulation to our attic. For my house, I figure it should pay for itself after two years (or sooner if we have terrible winters or summers ahead). There are a few things to consider when installing your own attic insulation.

Most home inspectors and online insulation calculators will tell you that you should have at least 12 inches of insulation in your attic in New England. We had 3 inches, not even enough to get to the top of the joists. 3 inches is about equivalent to R-9 insulation. (Insulation’s R- value indicates how well it insulates, with higher numbers being better.)

NOTE: By the way, it is easy to figure out what R- value corresponds to what insulation thickness: just divide the R- value by 3 to get the approximate thickness in inches.

So I decided to purchase 9.5 inch-thick unfaced insulation (R-30) to completely cover the existing faced insulation. Putting the new insulation on top of the old insulation should give at least 12 inches of total thickness. It turns out that the R-30 insulation I bought actually ended up being about 11 inches thick, so that’s even better.

First ask yourself this question:

“Will I need to be able to walk around in my attic after installing the insulation, or am I OK having the insulation too tall for walking around up there?
Adding a good amount of insulation can make it impossible to use your attic for anything (like storage or finishing the attic). If you want to be able to use your attic for storage or anything else, then you will have to either leave a portion of the attic with less insulation or build storage shelves that are higher than the new insulation. I have needed access to my attic in the past for adding ceiling fans to the upstairs bedrooms. However, my attic cannot be finished (too short – no standing room) and I have no plans at all in the future that will need attic access, so I am OK with having thick insulation that impedes any walking up there.

Tools / supplies needed

You will need these supplies for the best results on this job:

  • Insulation (unfaced if adding to pre-existing insulation, or faced if adding to an attic that does not already have insulation)
  • Scrap plywood/boards
  • Utility knife or box cutter
  • Filtered safety mask that will block fiberglass dust
  • Indirectly-ventilated goggles
  • Long-sleeved shirt & pants
  • Gloves

Getting ready for the project

Here are some basic things that need to be done in preparation for or during the insulation installation. Click any of the images below to enlarge them.

  • Inspect your attic
    Gap at side of gable vent
    Gap at side of gable vent
    Before you begin you should do a quick visual inspection of your attic to find any cracks, gaps, or other openings that are large enough to allow bugs or other pests into your attic. My gable vents already have screens to keep bugs out, but there were large gaps around the edges of the gables that I needed to seal. Use a weather-resistant, silicone-based caulk to seal these openings.
  • Buy insulation
    Many rolls of insulation purchased
    The rolls of R-30 insulation I purchased
    If you do not have any insulation already in your attic, then you will need to buy faced insulation (the paper-faced side goes down against the drywall). If you are adding to existing insulation, then buy unfaced insulation (i.e., no paper backing). Buy a few more rolls than you think you will need – you can return whatever you don’t use (as long as you haven’t opened the packages of the insulation you haven’t used).
  • Wear protective clothing
    Indirectly ventilated goggles
    Wear protective clothing, ventilation mask and goggles
    If you have ever dealt with rashes from working with insulation, then you know I’m not joking about the mask, goggles, gloves and long sleeved/legged clothes. You will be hurting big time if you don’t wear these. It is very important to protect your lungs, eyes, and skin from fiberglass dust (just imagine your lungs and eyes getting stabbed thousands of times with minuscule needles because your chose not to wear a mask or goggles). My respirator mask was filthy with dirt and dust after only 15 minutes in the attic.
  • Use some plywood sheets in the attic for convenience
    Plywood around attic access holePlywood sheet to sit / kneel on.
    Plywood for support around attic access hole and plywood sheet to sit / kneel on.
    If you don’t want to slip/trip and put a foot through the ceiling of the interior below you, then take some plywood into the attic. I had some scrap plywood lying around that I screwed to the joists directly around the attic access hole. It makes it much easier to enter & exit and gives you a place to put some tools. Other sheets of plywood are needed to walk & sit on while installing the insulation. It is also a good idea to have some wooden planks up there so you can easily walk/crawl around. It is also easier to cut the insulation on a piece of plywood.
  • Take breaks!
    My attic wasn’t very hot, but with the long sleeved/legged clothing I did sweat a lot and my clothes were soon drenched. The work is pretty easy and I never really felt too hot or too exhausted. However, even though I didn’t feel tired or hot and I was drinking plenty of water, I still started to feel one or two symptoms of heat exhaustion when I was getting toward the end of the project. Additionally, having to breath through the filtered mask for hours on end did start to feel a bit constricting. Make sure to take frequent breaks to minimize any problems with heat, dehydration and shortness of breath.

Adding insulation

Start early in the morning before your attic heats up. Plan on taking several hours to install the insulation. If you do not have standing room in your attic, then it will take even more time to carefully maneuver yourself and the unrolled insulation around while installing it.

The instructions included on the insulation wrapper were pretty straightforward and informative. I’ll include the package instructions here for reference:

Installation instructions from the insulation packaging
Installation instructions from the insulation packaging. Click image to enlarge.

If you are putting insulation in an attic that doesn’t have any insulation, then you would add the insulation between the joists, running parallel with them. If your attic already has insulation and you are adding more, then typically you would add the new insulation perpendicular to the old insulation and joists. I wasn’t sure at first which to do since my old insulation’s thickness only goes about half way up the joists. For me it worked out best to place the new insulation perpendicular to the joists anyway – it filled in the gap between the old insulation and the tops of the joists just fine.

Small attic entrancePulling insulation up through small attic entrance
Small attic entrance makes it difficult to bring insulation up.
Actually getting the insulation into the attic was the real trick! I only have one of those small closet access portals into the attic. The insulation would not fit through it while still rolled up in its packaging, so I had to open the packages and pull the unrolled insulation up.

  • Start installing in the far corner and lay it perpendicular to existing insulation
    Start installing in the far corner and lay it perpendicular to existing insulation
    Start installing the insulation in the corner furthest from from the attic entrance. The idea is that you don’t want to block yourself in, so you want to start far from the access hole so that you finish close to the access hole.
  • Leave some space between roof and new insulation
    Leave some space between roof and new insulation
    At the edges of the attic where the roof is at its lowest, make sure to leave enough space between the insulation and the roof so that there is good ventilation between the eaves/soffit below and the rest of the attic. Good airflow is important to keeping attics cool (summer and winter) and free from moisture.
  • Rolls of insulation installed with full contact between them
    Rolls of insulation installed with full contact between them
    Add the next row of insulation right up next to the first that you just laid. Side-by-side, they should be in very good contact for their entire lengths. You don’t want any gaps between them where heat can escape (winter) or enter (summer)
  • Warning: You should install insulation so that it does not come near light fixtures (the light fixtures for the rooms that are directly below the attic). Cut the insulation so that there is several inches of clearance around light fixtures. Some light fixtures do allow insulation to be placed directly over them – ask your local hardware store if you are unsure about your light fixtures.

  • Use a utility knife to cut the rolls of insulation to the appropriate length as you are laying it in place. You will quickly learn that the easiest way to cut insulation is to put it on a piece of wood, compress the insulation as much as you can, then slide the utility knife blade along the compressed area of the insulation. Use the same method when cutting the insulation to fit around obstacles in the attic (e.g., pipes, vents, etc.)
  • That’s all there really is to it. You just have to plan enough time and get it done.

Completed project

When I finished I still had to figure out what to do with the plywood that I had put in the attic. When I started the project I had actually taken several smaller pieces of plywood into the attic where I then assembled them into one larger piece (I could only fit small pieces through the attic entrance). After I finished the project I wondered, “Should I disassemble it and remove it?” To avoid disassembling the platform, I decided to leave it in the attic right by the attic entrance point and throw a couple small pieces of insulation on top of it.

Make sure to clean the room where you were entering/exiting the attic. There are probably lots of small bits of insulation stuck to the walls and floors. Also make sure to thoroughly clean your clothes, washing them a couple of times by themselves.

11 thoughts on “Installing attic insulation”

  1. Very thorough, & many important sigificant details like constructing a platform and leaving it in place for future trip to the attic, but most importantly…taking frequent breaks! Breathing through a filtered mask for long periods of time also restricts the access to fresh oxygen.

  2. I started laying down the new insulation on tip of the old one which very this maybe 2 inches. I did lay it down parallel instead of perpendicular; is that ok?

    1. Yes, it will be fine. Placing the insulation perpendicular helps it be more efficient. The gaps between insulation strips and the joists allow some heat (in the winter) or coolness (in the summer) to escape. Placing the strips parallel might mean that the gaps in the new insulation are directly over the gaps in the old insulation, still letting some of that nice temperature out of your home. You’ll still see a big improvement even if you put the insulation parallel. It isn’t worth it to go up there and change it all to perpendicular.

  3. Mike, some advice: Wood worm love plywood, it’s the bonding ply-glue which attracts them, so take the plywood bits out. Another tip the first INCH of insulation does 89% of the total heat saving and the next inch saves another 5%, whilst the extra inches up to 10 inches is money wasted. You are not supposed to know this informations, in a way its a trade secret to protect jobs, encourage heat -conservation etc, but if I was you I’d pick your extra insulation up and place it between the rafters above. It will do more good there and at least you will get a small return of some sorts. (this monetary saving is more myth than factm when did you last hear of anyone running to the bank with the cash in his hands but keep that to yourself) Another depressing message: Glass fibre is carcinogenic and banned, so do not spend too much time in the attic space. Cellulose chewed up newspaper is junk, so is spray foam, and double glazing not much use. Wearing two pair of trousers and an thick cardigan is the way too go, or copy the bears and hibernate for the winter?

  4. I’m preparing to add insulation. We have a split level ranch. the center of the attic has plywood over the insulation. Do I need to remove the flooring and add additional insulation. Can I replace the flooring afterwards. I’m wondering of pressing that extra insulation into the space under the floor will take away some of the insulation value.

    Also planning on installing new soffit vents. The existing ones are only small three inch circles and i don’t think there is enough air flow. Also I’m planning on installing the attic baffles to ensure ventilation from the soffits. I think alot of my existing insulation was blocking the air flow. Great blog post. Thanks.

    1. You’re correct, compressing the insulation under the plywood will take away some of the insulation’s abilities. You can add more insulation as long as you are not compressing it down. Absolutely you can use the same plywood after removing it, as long as there is nothing wrong with it (e.g., make sure there is no mold or rot).

      It does sound like you’re not getting enough ventilation. It sounds like you have a good plan.

  5. Mike, thanks for the article. At the edges of the attic did you just compress the insulation or did you cut in between each board to fit into the eaves?

    1. I just compressed it. It didn’t have to be compressed very much, because you need to make sure to leave a good sized gap between the top of the insulation and the roof so that air can circulate between the eaves and the rest of the attic (very important).

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