How to Insulate Your Basement: Part 3

[Music] [Music] [Music] well it's time for insulation now I'm treating insulation like it's a separate category for this video but the truth is that there is some overlap with the air sealing category that's because we want to choose a basement insulation that not only insulates the concrete walls but also offer some air sealing let me show you how it works now without getting too nerdy about this there's really one thing you need to understand about insulating a basement and that is that warm air can hold more moisture than cold air so when that warm air is cruising around the basement if it hits a cold surface it will drop that moisture now in a basement the relatively cold surface is the concrete wall sort of protect against that we are going to insulate the wall with rigid foam the ground is a pretty good insulator so you don't need a lot of insulation on basement walls in fact you can do the job well with just a two inch layer of polystyrene stuck right to the surface of the concrete although you can use plastic anchors to attach the foam I found an ordinary low expansion spray foam applied to the back of each sheet is more than enough to keep it stuck in place you'll want to keep pressure against the rigid foam until the spray foam tacks up usually no more than ten minutes which you can do by leaning a piece of lumber against the wall or using dried pieces of foam if there's something to wedge against when working around objects like this waste pipe you might need to work in smaller pieces now to cut multiple pieces of foam to the same size I stack in a line sheets make my cut on the top sheet using a circular saw and then repeat the process following the score mark left by the saw blade you'll notice that I have some gaps it'll need filling that's not due to sloppy measurements it's purposeful small gaps are hard to fill with foam so I leave them slightly oversize say about a quarter of an inch to allow me to get the tip of the spray foam gone in for easier filling if you already own a foam gun it's worth the $30 for a job like this it accepts large cans of foam can be dialed in to the size of foam bead desired and you can store partially you can of foam between jobs rather than tossing the leftover along the way somebody did some mayor sealing along the edge of the mudsill I like the effort but this spray foam is going to be in our way I'm going to cut it out flush with the edge of the mud sill using my notched trowel give the whole area good cleaning to remove dust that might get in the way of our foam adhesion and then apply a fresh bead of spray foam before sliding pieces of rigid foam into place against the mud sill this will insulate the top edge of the foundation wall and seal any air leaks coming in under that mud sill leave these pieces long they can be trimmed back layer once they set up the rim joist gets the same two inches of rigid foam insulation again sealed into place with spray foam a piece of vinyl tubing attached to the end of your foam gun is helpful for applying canned foam in these tight spots the idea here is that the layer of rigid foam creates an airtight insulated barrier that will help eliminate condensation between the indoor air and the cool surface of the lumber with condensation controlled you can then beef up the overall r-value with whatever insulation you'd like here I'm using a double layer of our 15 mineral wool batt insulation which I cut to size with an old corrugated bread knife the mineral wool combined with the foam gives me an hour value of about 40 remember the rim joist is above grade so unlike the concrete walls it needs to be insulated at at least the same r-value is the framed walls above it after the canned foam is set up trim it flush with a notch trowel to leave a clean finished surface you can also trim off the overhanging foam from the top of the wall using either the knotch trowel or a handsaw with everything trimmed back look for voids that need to be filled don't be afraid to plunge the tip of the spray foam gun right into a hole to fill it completely the goal here is to stop moist air from finding cool concrete for tighter seams and gaps use house wrap tape make sure the surfaces are free of dust roll out the tape neat and then smooth it out with some firm hand pressure or a stiff blade to ensure a good bond that wraps up the job and now you have a dry comfortable efficient space ready for stud walls and your desired finishing touches [Music] you

Channel: finehomebuilding

Views: 169,399

Keywords: Basement, Basement insulation, Insulation, Masonry walls, rim joist, batt insulation

Id: v2QMBU8yS-I

Length: 5min 7sec (307 seconds)

Published: Wed Jul 01 2020