I am designing my own home and it will be a single storey with full  basement (main and basement built from ICF blocks).  My questions is on the roof (see attached pictures).  At present if you look on the roof on the left side of the entry there is a large amount of roof area that will direct rain, snow, etc into one drain point, my thought is that this is probably not a good idea????  Am I being over cautious or is this a real problem, second if it is a real problem does anyone have a suggestion as to another entry way roof design which keeps a similar look to the overall building?

I would like to send this off to the truss manufacturer to get a quote asap, so any replies would be appreciated.

Thanks

The biggest issue is keeping the water out of your basement. Backfilling and drain lines with washed stone and PVC pipe will help, but there are occasions where foundations drains fail - occasionally they can get clogged at the outlet. I'd suggest that you install a surface drain right where the water will land, connected to a pipe to get the water away from the area. Keeping it seperate from the foundation drains will help insure that they aren't overwhelmed by the water.

Of course, as with any house the final grade should slope away from the building so surface water doesn't inundate the basement.

As stated above another safety measure wouldn't be a bad idea. Lot of water coming off the roof in the back!

Thanks for the comments.  I am not too worried about getting the water away from the building, we are located on  a farm so I have lots of room and options to deal with that aspect but obviously an important one. 

Am I correct in understanding that no one feels that there will be roof issues i.e. premature wear on shingles, water wanting to penetrate under the shingles, near the valley, ice dams, etc in this area?

Jojo,

In situations like this, I have used the system suggested by Bob and it worked well.  To augment this I had metal flashing installed in the valley and that covered with W. R. Grace Ice and Water Shield (peel and stick).

This roof design is creating quite a watershed on the left side that is restricted by the roof.   Just to be safe I think you should install a catch basin with grate on each side of the entry way to keep water from being trapped by the foundation.  Valleys are weak areas in a roof that are subject to flexing.  Too much flexing will tear the Ice and Water Shield.  That is why I reinforce the valley with metal flashing.

The other problem with valleys is ice dams. Melting snow from quote a bit of the roof lands there so you can get terrific ice dams which will back up and leak. However, since you're ovbviously on this forum and familiar with ICF's I assume your're using raised heel trusses or some other tested method to keep the roof cool and avoid the whole ice dam issue.

Spray foaming the roof decking from inside the attic should keep the heat from melting the snow from the bottom side and then refreezing during the night.  Dana1 could probably give you some insight into what methods will prevent ice dams.

and the ZIP code for this location is...?

Big roof valleys of shallow pitch don't really cut it in heavy-snow country, because even when the rest of the roof has 8" of snow on it, depending on wind currents you could have 30" of snow in the valley, which has a significant R-value. Then, the structural timbers supporting the base of the valley creates a thermal short, making a localize R-value minima at the identical location where the snow has a R maxima. As outdoor temperatures rise from arctic levels you're almost guaranteed to get meltwater going on in the valley while it's still WELL below freezing outside- not so good...

I despise massive use of Ice & Water shield on the structural roof as a band-aid, since that brings the outward drying capacity of the assembly to ZERO. Don't go there except as a last resort, and even then... Metal flashing in the valleys, with a strip of I & W, sure. If you "need" it 4' up both sides of the valley, you have a "solution-problem" to be dealt with.

With good thermal breaks from structural members and high clear-assembly R the heat leakage from interior won't be the source of temperature differences across the roof deck big enough to cause melt/re-freeze issues, but the sun and uneven snow depths are guaranteed to create at least a minor problem. Steeper roof & valley pitches will help some, even without going to a "lightning-splitter" 14/12 or higher pitch. The wider than 90 degree angles on some of the knit lines of this roof make for some relatively shallow valley pitches, whereas the narrower than 90 knits make for narrow snow-traps- it's a damned if you do, damned if you don't kind of deal. But if it's steep enough to drain or shed snow, and high-R enough that the interior temps aren't the primary source of temp difference, ice dams can be minimized. (It's a lot easier to deal with a simple gable or shed roof setup than multiple valleys & pitches though.)

First-measures: Put a significant fraction of the total R as rigid foam above the roof deck, and design the interior R to be vapor-semi-permeable, to limit winter moisture accumulation in the roof deck, and let it dry seasonally toward the interior. Make the total R at LEAST R50, independent of code-minimums that might be lower. The fraction of exterior foam R to interior R necessary needs to be designed for the specific climate (but 50/50 works for the vast majority of the lower48 of the US.) Nailbase iso or EPS panels through-screwed the the structural deck are available from a number of vendors, but a SIP approach can also work.

Secondary, but still important: Put a secondary nailer deck on 3/4" furring above your exterior foam to hold your shingles, so that you have a ventilation gap under the nailer. This gives any meltwater dribbles from the uneven solar gains across the roof a secondary escape route, while evening out the roof temps somewhat, and gives the nailer decks a vented drying channel. This is pretty much the same concept as vented rainscreen gaps behind siding on walls, but the gap needs more cross sectional area than walls, since seasonal moisture drives from wet snowy roofs can be much higher than walls. (3/4" rather than 3/8" ) Both Atlas and Hunter (and probably some otheres) sell ventilated nailbase insulating roof panels, but a DIY with furring can also work.

Building in a drainage with a small valley-capture basin and buried drain directing the water either to a drywell or daylighted well away from the foundation isn't a bad idea either. I had to retrofit such a system at my cute antique of a bungalow to keep the foundation dry enough in that corner that I could safely insulate it from the interior. I used 2" XPS under 10-mil poly (bonded to the foundation with roofing cement) under 6-10" 3/4" screenings, and flexible 4" drain tile daylighted in a down-slope garden bed for one valley, and to a drywell for the other. The XPS limits the frost-heave potential at that somewhat moister soil location. I'm not sure it was really necessary, but it seemed like cheap insurance. The rest of the (hipped) roof has no gutters, but a 26" overhang , with a more standard "French drain" approach under the drip lines for 90% of it (and concrete splash pad on the driveway side.)

Thanks for the info the location is in Sask Canada.

The information with respect to placing rigid foam on the surface of the roof deck (if I am correct in the understanding) seems to me to be a significant amount of additional work and cost?  If this is really the only way to make this system work then I would much rather look at a redesign of the roof lines around the entry way, and would appreciate if anyone has  any thoughts on how to accomplish this while maintaining a somewhat similar appearance.

Thanks

Posted By jojo12 on 02 Feb 2011 08:47 PM
Thanks for the info the location is in Sask Canada.

The information with respect to placing rigid foam on the surface of the roof deck (if I am correct in the understanding) seems to me to be a significant amount of additional work and cost?  If this is really the only way to make this system work then I would much rather look at a redesign of the roof lines around the entry way, and would appreciate if anyone has  any thoughts on how to accomplish this while maintaining a somewhat similar appearance.

Thanks

Which is your nearest weather station on this list?

http://climate.weatheroffice.gc.ca/climate_normals/results_e.html?Province=ALL&StationName=scott&SearchType=BeginsWith&LocateBy=Province&Proximity=25&ProximityFrom=City&StationNumber=&IDType=MSC&CityName=&ParkName=&LatitudeDegrees=&LatitudeMinutes=&LongitudeDegrees=&LongitudeMinutes=&NormalsClass=A&SelNormals=&StnId=3259&

Not sure if it matters or not, but the truss manufacturer doesn't see any issues with it, not sure that they look at all issues or just structural?

With an average January outdoor temp of about -17C, and an a +21C/30% RH conditioned space temp you'd need at about 50% of the total R , maybe a bit more above the roof deck to use a highly permeable fiber-only approach on the interior. That's doable, but it could be cumbersome to build at high-R.

Alternatively, if you put about 1-perm shot of spray foam on the interior of the roof deck (~5cm of 2lb foam) you can cut the exterior foam down to about a quarter or third of the total, and fill in the rest on the interior with cheap fiber, no interior vapor barrier.

eg. For design goal of R50+:

Roofing/vent channel/R20 iso panel/roof deck/R12 SPF/R20 batts or spray cellulose, etc. ==> R52

or

Roofing/vent channel/R10 XPS/R26 Icynene MD-R-200 mid density/R20 batts ==> R56

In the first stackup the interior of the SPF is the condensing surface, but it spend more hours above the dew point of the interior air than below it, even in winter, and no damage is done. The SPF limits the accumulation of moisture in the roof deck due to it's somewhat low permeabilty, but is permeable enough to dry toward the interior. Since the foam won't wick condensation toward the wood, and no condensation forms on the wood directly, moisture only gets in via diffusion through the SPF. With R20 of thermal break on the truss elements the localized melting due to the thermal short is practically non-existent.

In the second stackup an even larger fraction of the total R is foam, so the condensing hours at the inner face of the Icynene is even less, and with some vent-gap above the XPS the roof deck would dry in both directions at about 1-perm each side. There's some amount of striping melt potential due to the lesser thermal break over the trusses, but it's pretty minimal.

In both stackups the majority of the R is exterior foam. This is probably overkill for the climate and it might be rebalanced toward fiber for a more economical stackup modeling it with WUFI model to ensure the roof decking stays try enough.

Midwestern snow pack isn't usually as deep or dense as maritime snows, so the overall ice-dam risk isn't huge, but in your climate there's a good argument for at least R10 outsulation (a double layer of R5 XPS with lapped seams works), and at least R50 of total attic insulation. R75 is probably economic, if a vented attic all-cellulose approach is taken, but it has to be done very well at the attic floor to minimize ice dam issues (and you DON'T want ice dams backing up and dripping onto a half-meter of cellulose for weeks before discovering the ugly sticky truth.)

You dont need to put on a secondary roof plane or redesign your roof. Best practice? Maybe. There are tens of thousands of homes with valleys such as this. I have reroofed tons of homes in cold climate snow country that have exhibited no rot, leakage or deterioration at this junction. 4/12 or steeper. We roof with one width of ice water up the valley, one width of 20" flashing up the valley and then a closed cut valley. If there is a large expansion of roof spilling into the valley then an open valley with a v crimped center is used. The homes that have ice dam problems are usually poorly detailed vaults or are leaky at walls/plates/openings into the attic, windwashed insualtion voids, ect. The bigger issue to me is the weight of the snow that can pile up at pitch changes in valleys. Depending on site you could have some major accumulation there.

Take a drive around in a newer subdivision and look for yourself. Find homes that have ice dams and note age, style, ect. You should be able to pattern the problem with regard to different style roofs and problem areas.

With respect to your roof design, I assume a software hangup has your main hip roof over the living area slightly out of plane with what I assume is the bedroom area gable.While technically buildable that little mini valley is a complete waste of money and unnecessary. The shallow shed roof between the valleys is another snow collection area, do you need those gables? Eliminating those two gables and the shed roof and going with a bigger hip set will cost much less, be cheaper to build and eliminate the shallow to higher pitch which can look odd.

Posted By greentree on 06 Feb 2011 12:36 PM 
Eliminating those two gables and the shed roof and going with a bigger hip set will cost much less, be cheaper to build and eliminate the shallow to higher pitch which can look odd.

It will not cost less to build ................... and you have created more eave area, which is the problem spot

Well Chris, I will have to respectfully disagree with you. A bigger hipset will cost less than a hipset with a shed roof and 2 gables on one side of it from a truss company, I think that's fairly obvious. The more complicated it is, the more pieces, more design, more assembly.

Creating valleys to have less eave is a rather dumb idea, eaves aren't a problem, it's uncontrolled air leakage and inadequate insulation at the wall plate.

Posted By greentree on 07 Feb 2011 08:49 AM
Well Chris, I will have to respectfully disagree with you. A bigger hipset will cost less than a hipset with a shed roof and 2 gables on one side of it from a truss company, I think that's fairly obvious. The more complicated it is, the more pieces, more design, more assembly.

Creating valleys to have less eave is a rather dumb idea, eaves aren't a problem, it's uncontrolled air leakage and inadequate insulation at the wall plate.

your thought are ramdom an scattered,

A gambrel roof is desired for a particular look, if you want a similar look with a hip then it would be a mansard roof. Which is of course more materials = more money

I frankly don't know where you are coming from .......... a hip has many more pieces than a simple gable roof when considering the same pitch and a gambrel is not limited to a low pitch gable

That roof is complex enough that a good framing crew may be competitive with the truss manufacturer plus installer. I would quote it both ways. I would not build that roof in snow country, if I did I would specify a higher live load for the roof, as there are several areas where snow will likely drift.

Any roof can be made to not leak. A simple roof line makes it easier and cheaper. When did we get our aesthetics so out of whack that a house with 19 separate roof planes is the norm?

cheers
Eric

Chris,
His drawing has neither a mansard or gambrel. He basically has a hipped roof with some gables on it, and some full gable areas. I'm not sure how you as a builder cannot make the distinction, maybe try googling the terms so you can see a correct example.

Taking it beyond a pretty picture and into a framing view a full hipset from a truss plant extending to the backwall would be much cheaper than incorporating a shed roof into the main hip truss' creating a nonstandard truss, PLUS two gable sets, again I'm talking from a truss plant, not stick framing. If the two gables in back are supposed to be vaulted then it's even more complex and costly. Again I'm talking strictly from a full truss order and set. Stick framing changes everything depending on bearing.

Obviously we aren't seeing eye to eye, could be regional differences or you don't do many truss sets.

As Eric said, the simpler the roof line the cheaper it is, period.

So If I understand this correctly the general conversation is that I would be cheaper from a complete truss package perspective to go with someting as shown in the attached picture. I think I have issues because I now have a worse valley.
A second question is there any drafts people/ architects that would have time to finalize this plan (I believe I have it near complete, the only thing is I dont have a handle on the roof design part, and I need someone to check the framing and supports and put it in a quote/blueprint format
so I can start getting materials ordered. I have the full plans drawn up in Chief Architect at present. Please advise on your cost or contact. Thanks