Non-vented roof: plan reviewer says no!
As I feared, the city of Toronto building department has apparently issued an official edict that they want ventilation under roof sheathing, like the Ontario Building Code asks for, PERIOD. You will NOT get away without this ventilation if you use a draft sealing method of insulation like blown foam or dense-packed cellulose. No amount of argument will shift these folks- they’ve made up their minds for some reason or another and won’t be persuaded otherwise.
I have a rotten little 6’x6′ patch of hip roof planned for the corner of my addition, to mirror the existing (non-vented) hip roof section on the opposite side of the existing house. The part of the house in question is 1.5 storeys and there’s no vented “knee wall closet” under this particular roof section- the ceiling finish is attached to the underside of the rafters (i.e. cathedral ceiling style) and I’d like to do the same in the addition. The hip roof section intersects dormer walls on the east and south sides (and rests on short walls facing south and west) , so there’s not really any place to vent it to. I guess I could plan to furr out the hip jack rafters with 2x2s running perpendicular to them to attach the sheathing to and then put in an unsightly attic vent on each side of the hip rafter near the peak, but I really don’t want to do that- it would really look ugly.
So when I submitted the plans, I noted that the roof was impractical to vent so it would be insulated with spray foam and completely covered with ice and water shield. The roof section faces north and west (shaded most of the day on that side) so I’m not worried about cooking the shingles. Unfortunately the city will not accept it, period. I have to find some way to vent that stupid little section of roof or I have to build it the way I planned and roll the dice with the inspector…not a pleasant thought as he can order me to rip it out and re-do it…
Any bright ideas out there?!
Replies
MM, down here in the state of Massachusetts if you don't believe a municipality is being fair in the way they're applying the code you can appeal it to the state level. I think the process is to first get officially denied a permit, then send any evidence (trade journal articles, etc) to the state. Maybe same thing up there in Canada?
around here the code enforcer can be over ridden by a license P.E.
They want a P.Eng. to review my roof structure too, so I'll ask him what he thinks, but I'm not too hopeful. These plan reviewers in my experience are code ####- if the code says to do something they want it done that way, and no alternative which serves the same intent will be acceptable. The inspectors can be just as bad, or they can cut you some slack, but it's the luck of the draw.
A P.Eng. SHOULD be able to over-ride the code if he takes professional responsibility (and liability) for the decision and can show that what he's proposing meets the design intent of the code in another way. In the design of the basic structure, there's a section of the code where the P.Eng. can analyze whatever structure is proposed and determine by calculation whether or not it will handle all the design loads- but in areas like providing venting under the sheathing there is basically no equivalent to that.
They were quite specific about having officially decided that they would not accept foam as an alternative to venting- I wonder if they had some bad experiences with poorly-installed unvented roofs and just said "no more"?! Good thing I anticipated this for the entire rest of the roof and provided a vent space!
Seriously: any suggestions on novel ways to vent this little hip roof to keep the code #### happy? I can post a sketch if that would help...
You could always fake it. Install dummy soffit and ridge vents. To the inspector they will look like the real thing but you will know better.
yeah.. post the sketch....
we did a lot of venting shed roofs that terminate against sidewalls..
there are a lot of ways to skin your cat...
i've vented just about everything under the sun....
now i just dens-pak the ones that are impractical... our inspector doesn't mind well detailed hot roofsMike Smith Rhode Island : Design / Build / Repair / Restore
Here it is, Mike. This is a front elevation of the place as planned. The hip roof in question occupies the square patch between the "gable wall" of the addition's shed-roofed "dormer", and the gable-roofed dormer wall to the left. The hip roof is only ~ 6'x6' plus overhang. Now you see my dilemma- the hip terminates at vertical walls on both sides and has no ridge to vent to, with a hip rafter separating it into two triangular sections of roof which will need to be vented separately.
I'd thought of furring out the hip jack rafters and the dormer wall studs to produce a venting space behind the wall sheathing up to the soffits, but that would be a royal PITA and I'm looking for another way. And you can see that vent hoods on either side of the hip rafter near the peak of this little roof would look very ugly.
Man, I wish these plan reviewer people would listen to reason and let me foam out this little roof. I'd do the other one in the existing house at the same time- probably has mineral wool in it now with no VB and really should have been vented, and there's no real way to deal with it either. Fortunately the plan guys can't force me to change anything in the existing house...
molt... from the one view & your description.... i'm assuming the hip is two-sided regular pitch... not including the overhang.. each fascia is 6'
so the hip (ridge) from the view looks like it is about 10' ..
use the same baffled ridge on the hip that you do on your ridge..
i like the AirVent II, shingle over ridge vent.. it has a low profile, it has a baffle, it has a filter fabric liner ( keeps snow & bugs out ) and it looks good
i'd terminate it right in the upper corner with a neat color coordinated aluminum flashing.... your soffit vents will be the continuous style... and each jack rafter bay will vent to the hip
i mean, if they are gonna make you vent it.... that's how i'd do it
Mike Smith Rhode Island : Design / Build / Repair / Restore
Edited 1/19/2005 5:42 pm ET by Mike Smith
Mike: yes, you've got the picture exactly.
I had a look at the Air Vent II (Shingle Vent II) unit on their website and it looks like a great product for the main, horizontal roof ridge, but I'd never thought of putting such a vent directly on my hip roof ridge- I just assumed that it would leak.
Would it do a good job of keeping out snow and rain, even in the down-sloping position? Unlike the vent at the main ridge, I can imagine that this one would spend a good part of the winter completely covered with snow, which would be rough business when it started to melt- pretty tough to keep the meltwater out. Have you vented hip roof ridges like this before without leaks? I guess I'll contact them and ask if they warrant the product for hip roof ridges- can't hurt to ask!
I haven't seen a cross-section of one of these ridge vents, but I imagine it has more than one vertical baffle with a channel in-between them. I assume that if anything did get in past the first baffle it would just drain down the length of the vent and drip off the drip ledge into the eavestrough at the corner- is that the idea? I guess on a horizontal ridge you'd cap the ends or shingle over them in the overhang area, but here you would just leave the bottom end open or screen it in somehow to keep the wasps out.
I'd already figured I'd want to cover that entire roof section with ice and water shield, but are there any other tricks with respect to caulking etc. to keep such a ridge vent installation leak-tight? If I time things right with respect to the inspections, I might even be able to install the ridge vent over top of the ice and water shield and accidentally forget to cut a venting slot in it first...If I then foamed the rafter bays I'd end up getting basically exactly what I wanted in the first place, at the cost of some cardboard insulation baffles and a little extra rafter depth...Maybe there's more than one way to skin this particular cat!
Thanks for the tip, Mike- I think doing this will be easier than fighting city hall...
yes.. there are a couple of tricks.. one in particular.. is similar to a metal valley...
in a metal valley, you use a "hem" at the edge.. the shingles go over the hem.. any water blown up the side of the valley, hits the hem and gets sent back down by gravity
the same thing is true of the ridge vent..
the ridge vent sits on top of the asphalt shingles....if you fold the felt back over the top of the shingle, it forms a "hem" any water blown thru the edge of the ridge hits the "hem" and runs back out onto the shingles
i sorta doubt that Shingle Vent, or any other mfr., is going to warrant this installation on a hip... but i don't see why it should leak
i can't post any drawings on this computer, but if you email me a fax number i can fax you a sketch of the installation i'm talking about
my email is
mfsmith1 (AT) cox.net
that's the office, so, i'll get tomorrow
as for leaving the ice & water in place over the slot... hey, great idea..
as long as it can't be seen from the attic... because you can actually see if a ridge vent is open or not
and last , but not least.... NO, i have NEVER done this , but i do know that hips that dead end into vertical walls HAVE been ventilated by others...
Mike Smith Rhode Island : Design / Build / Repair / Restore
Thanks Mike- e-mail with my fax number's been sent to your office address.
If I can work the inspection timings so that the inspector never sees the thing shingled before it's insulated, that would keep him from noticing the missing vent gap in my ice and water shield and I'd be away to the races. I can be a devious b*stard when I need to be, especially when someone's being unreasonable with me!
But in case I can't get away with it, I'll still have to install this sucker properly so it won't leak- Mike's detail sketch will help out big time. But I'm still a bit nervous about this- anyone out there vented a hip roof at the ridge like this before and been successful with it in a snowy climate?