What is roofing felt or underlay?

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Unless you have a problem with your roof, you may never need to know what roofing underfelt or underlay is.

So what is underlayment or roofing underfelt? Well, underlay sits on the roof rafters, underneath the battens and tiles. It provides a layer of insulation and an extra waterproof barrier for any moisture which gets under the roof covering. It also protects the roof against wind-driven rain getting through the tiles and it also drives any rainwater that has leaked between the tiles back to the gutter.

The underlayment needs to be treated with care to make sure it stays in good condition. If roofing felt gets damaged or torn – whether by furniture or people scraping into it – then the roof’s water tightness is compromised and it could leak. It’s really important to get tears mended immediately and to check it regularly for wear and tear, just as you should the outside of your roof.

Small tears can be repaired using roofing felt adhesive and a piece of felt as a patch, but only if you are sure this is the source of the leak. If, for example, the underfelt is often wet, then you need to investigate the roof for the cause of the leak. Rainwater should only get through to the felt in exceptional driving rain. 

If you are not sure, then get a professional roofing contractor to give your roof a thorough check.

DIY Roofing Underlayment Installation

Here is something for you, if you are more into video

Installing Roofing Underlayment Yourself

Good afternoon, ladies and gentlemen, today, on your average roofer, I’m going to be showing you guys how to properly install your ice and water shield membrane and your synthetic underlayment. Let’s get right to it before we get into today’s video. I want to give a big thank you to today’s video sponsor ups drive. Ups drive connects the future trade professionals of America with industry experts for a personalized, one-on-one tutoring experience expert guidance that you need to pass your trade exam and get your license. They will work with you, one-on-one for exam preparation for multiple different trades. Tutors you are paired with are either still working as professionals or retired trade professionals, and they are experts in their field.

Students can go to their website and pick a specific trade and they will be matched with the appropriate tutor. Upstrive sells all the books and study materials that you will need to help with your trade exams. Upstrive hires experienced trade professionals as their tutors. You can become an up strive tutor by applying online on their website, but that’s it for today’s sponsor. Let’s get right to the video, so the first thing you want to do after you rip your entire roof off. You want to make sure, there are no nails that are penetrating the roof that is going to stick up and catch your underlayment. What that’s going to do is it’s going to cause holes in your underlayment from the underside up, and you guys definitely don’t want that. I like to install my ice and water shield before my drip edge.

The reason I do that is so I have full coverage on the plywood if I was to put my drip edge here. First, um there’s two inches of exposed, plywood and any ice damming that backs up out of your trough may cause uh damage on the bottom sheet of your plywood. You don’t want to do that. So the first thing you want to do is slide your ice and water shield right to the very bottom of your plywood. Don’t worry about it being a little longer as you guys can see. This underlayment wasn’t cut perfectly straight.

Just leave a little bit of overhang on that and you’ll be able to cut that straight to the plywood after so the first thing, you’re going to want to do is you’re going to want to take your ice and water shield the backing on one side either the Top of the bottom pull it back out of your way, make sure you’re still flush on your plywood and you’re gonna go ahead and tack that into place roll the underlayment back on itself, so you can get that paper and roll it along the roof. If you’re on a steeper pitch roof, obviously you’re going to want to do this in smaller pieces, which is fine. But if you’re going to do that, make sure when you have a seam on your ice and water shield, you overlap it onto itself about 10 inches.

That way, you got full coverage and uh and no seam lines, but what you’re going to do here is run it out, and once you have it flush to the bottom of your plywood again you’re going to go ahead and nail the top all the way across so once you get down to the far gable of your roof. You’re gonna have to cut this off. There are two ways of doing this: you can either roll it past and cut it off, or you can kind of flip it back on itself, roll it to the edge of the roof kind of smush it down and you’ll see a little bit of a seam line. That’s kind of a rough estimate of where you want it to be and go ahead and cut that off make sure your remaining paper comes off as well and, like I was saying you have this edge, that’s overhanging a little bit just go ahead. Take your straight blade or hook blade, run it right along the edge of the plywood, and cut that off perfectly straight

Once you have everything cut off, you have it square, you have it exactly where you want it you’re going to go ahead and lift it up, Grab the bottom side of the paper and pull it right off, and that way once this gets hot in the sunlight. It’s going to adhere directly with this car directly to your plywood, and it’s going to protect you from any ice damming on your roof. Now that you have all your paper ripped off, you can go ahead and nail the remaining parts along the bottom. Do that all the way down the roof? That way you have this fully attached to the decking and then you’re going to go ahead and get your synthetic underlayment. I’m going to show you the proper way to do that because a lot of guys make a common mistake and I see it on multiple roofs. We rip off roofs all the time and there’s always one big mistake that is costly to the homeowner. In the long run, So I’m going to show you how to do it the proper way.

The common problem we always see when we’re ripping off roofs is people Will put their ice and water shield directly onto the decking and then they’ll shingle, their bottom five courses, which will cover that ice and water shield. The problem is when you rip that roof off the backings on all these shingles are going to be stuck to this ice and water shield. Once this heats up in the sun, it becomes tarry and sticky. These shingles will stick to it. So what will happen is when you rip off the roof. You’re only going to be able to get the bottom half of your shingle off and if you only get that off you’re leaving this whole backing on there, which is going to create a little bit of hump in your roof.

So the way to avoid that is actually putting your synthetic underlayment over top of your ice and water shield. The ice and water shield is going to give you your protection from ice damming and your synthetic underlayment is just an added layer of protection, and it’s also going to save you money down the road because when the next roofer comes to rip off your roof if You can’t get these shingles off he’s either going to go over it and it’s not gonna be uh, appealing to the naked eye or he’s not gonna rip. These off and he’s gonna have to rip off the whole bottom sheet of plywood and it’s gonna cost. You have a lot of money in the long term, so just spend the extra 75 for an extra roll of synthetic underlayment and I’ll show you how to install that and protect your roof in the long run. So, as for installing your synthetic underlayment, you’re going to go ahead and do the same thing, you can run this one a little bit higher than flush on the bottom of the plywood, because you do have your icing water shield there and you’re gonna be putting drip edge over it that way, it’s just it’s easier for you to keep straight and the same thing as the ice and water shield because this paper wasn’t cut off straight by the last guy that used it.

You just go ahead, leave a little bit of overhang that you can cut off after you’re, going to put one nail and tack it in place and you’re going to do the same thing. That’s the icy water shield, you’re going to run it out, make sure you’re. Following a straight line, as you can see, I left about a quarter-inch of an overhang there and you’re going to go ahead and nail it into place and, as you can see, the reason I only tacked one corner was for when I got down to that End I had, uh, I had room to adjust my paper back and forth, but now that I can see, I got it straight. I can go ahead and come back here, pull my paper tight and keep it flat to the roof deck and put my nails into place, as I normally would all the way across the roof. As you can see, my paper is laying perfectly flat so now we’re getting down. To this end, we’re going to do the same thing as the ice and water shield, we’re going to come over the gable and just run our knife.

[ Music ] go ahead and run our knife flush against the plywood. That way, we got a nice straight line. Our drip edge will sit over the top of this and you’ll nail that into place as it sits. So that’s the basics for starting your synthetic underlayment on your roof. This will protect your shingles for the next guy that has to rip them off. Won’t damage your house and cost you more money. If you’re going to continue this underlayment the rest of the way up,

Your roof, which is obviously highly recommended they have these lines in the roofing synthetic underlayment. What these lines are here for this thick line here and there’s also one up there at the top. That’s for your overlap! So when you’re running this on your roof, your next one is going to drop down that three inches, so they’ll overlap that three inches. So this piece would be obviously your next course up, but it will overlap down to that black line and that’s how you make sure you have the proper overlap on your synthetic underlayment. Now, you’ve got your ice and water shield and synthetic underlayment covering your entire roof deck you’re going to go ahead.

Take all your roof flashings, all your drip edge and you’re going to go ahead and you’re going to go ahead and you’re going to install those along all the eaves and along all the gables. So there you guys go that’s the basics for installing ice and water shield and synthetic underlayment on your roof. It’s definitely worth your investment. It’s about 75 dollars a roll. It covers about a thousand square feet of roof decking! It’s fairly inexpensive! It’s going to protect your home, make your home and your roof last a lot longer just spend the extra money do it properly and, like I said, always overlap it over your ice and water shield, because down the road when you’re ripping this roof off, you won’t Be getting those shingles off the ice and water shield put the synthetic over it, the shingles will come off.

You can take off the synthetic underlayment, redo an ice and water shield and there’s not going to be a bump in your roof. It’s going to make your house look a lot nicer, it’s going to make the job a lot easier and it’s going to save you money in the long run. Remember guys if you like this video be sure to like and subscribe, you don’t have to be the best, it’s all right to be average.

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