How to Vent a Bath Fan Through the Roof | This Old House

our story today takes us up on a roof let me show you what i have back here i have a fascia and overhang which is the soffit underneath here and these vented pieces right here are perforated pieces they're actually a soffit vent it's designed to take the cooler air from under the overhang into the attic let me show you where it goes now i'm here at the highest part of the roof the ridge underneath these shingles right here there's a slot on the roof that runs the entire length that's called a ridge vent it's designed to let the hot air of the attic out pulling the cooler air from the soffit vents into the attic unfortunately it's pulling more than just cool air into the attic now back here under the overhang there's another kind of vent this one right here and this is a vent from the bathroom fan and it should never be in a vented soffit it's causing the homeowners a lot of problems okay tommy let me show you what we have here okay a few months ago i put in a new bathroom fan and we noticed this discoloration in these areas right here under the roof sheathing that's right that's the beginning of mold so what you've done is you've actually vented the bathroom fan outside but you vented into a vented soffit what happens is that soffit pulls that warm moist air into the attic in the winter time it condenses under the shading causing the sheathing to get wet causes mold to grow that's as bad as venting the fan right into the attic okay so what can we do about that well let's take a more direct route and vent the fan right out through the roof all right sounds great now the best way to mark for where we're going to put the hole is about in the middle of the rafter bay i'm going to take a nail and i'm going to drive it right through the roof sheathing through the roof shingles and it'll stick up we'll go outside locate the nail all right we're up on the roof and you can see where the nail came through the roof and this is where we're going to drill our hole we're going to use this vent hood right here it actually has a little door on the inside here that will close with gravity to keep the cold air from blowing back into the bathroom when the fan is off it has a screen right here to keep the critters out first thing i want to do is remove some of the roof shingles so i can drill a hole all right now i'm going to measure the vent hood it's five and a half inches so what i'm going to do is i'm going to set my tape at two and three quarters out on one side five and a half on the other side and that will center my vent hood right over the nail now cut right across the bottom here now remove that shingle okay now i gotta break the seal of the shingle so i can slide the vent hood up under the shingles now all right that fits good now i'm ready to drill a hole i'm going to use a four and a quarter inch hole saw okay now ready for the duck now your original duck work is actually uninsulated so what i want to do is i want to change it to this right here an insulated duct system by doing that will lessen the chance of condensation forming in the winter when your attic is cold now i want to put this sleeve into the pipe so i can connect the ductwork to the roof first thing i need to do is i need to crimp this so it will fit inside the pipe by crimping this pipe it actually makes it smaller so it'll fit in for four inch pipe all right now it'll fit inside this four inch pipe slide it right on there okay now to hold the two together i'm gonna use this foil duct tape all right that's good this is the end that you'll pass to me when i get up on the roof while i get up on the roof disconnect the old work and connect this one okay okay slide it up all right tom all right now to hold the ductwork into position i'm simply going to cut a couple of tabs on each side so i can nail it to the roof now bend those over now slide the ductwork down just a little hold it right there let me get a nail that's one all right now we're ready for the vent hood now what i want to do is i want to run a bead of caulking right around the perimeter underneath a nice heavy bead of a tri-polymer caulking seal it up really nice okay now i don't want to put any on the bottom right here because if any condensation should form it'll run out under the hood i gotta pick up the shingle slide it right up in there push it down work it around make a nice tight seal good now what i want to do is pick up the shingle then i'm going to drive the nail through the flange into the sheeting okay now the other side okay now i want to put another bead of sealant right down here nice thick bead soften it right at the edge of the roof shingle push that shingle right in it that'll seal that do the same thing on the other side cross the bottom of the shingle a little bit push it into it now i want to put a couple of nails across the top of the vent hood okay nice thick bead there across the top of the hood now just push the shingle into it and the vent hood is sealed now when you turn on that bathroom fan all that warm moist air will come out of the house and stay out of the house tommy this is great i'm so appreciative you did a terrific job thank you my pleasure

Channel: This Old House

Views: 2,746,290

Rating: 4.8765955 out of 5

Keywords: This Old House, Ask This Old House, DIY, Home Improvement, DIY Ideas, Renovation, Renovation Ideas, How To Fix, How To Install, How To Build, Roof, fan, vent fan, installation, Do It Yourself, Through, bath fan, roof mounted, episode part, episode, Tom Silva, Ventilation, tom silva this old house, tom silva house, tom silva construction, tom silva tools, tommy silva

Id: PqrZWd_CQIE

Length: 7min 29sec (449 seconds)

Published: Mon Aug 04 2014