I have a roughly 40 year old home. Every winter I get some ice damning in the gutters backing up a bit onto the roof. The roofing shingles and decking I replaced myself 4 years ago. I have snow and ice shield running up the roof sheathing extending two feet past my interior walls. The interior house has no cathedral ceilings and all the ceilings are drywall with latex paint.
I have no visible signs of damage either in the house or in the attic but I know that doesn’t mean there is no damage or that it won’t cause damage if I don’t remedy the situation sooner rather than later.
My solution in part is as follows based on information from these and other forums, as well as the Building Science web site and the Building Materials and Wood Technology web site at UMass (Paul Fisette articles).
The first step I plan on taking is to install 2×2 furring inside each rafter bay tight to the underside of the roof deck. I’ll then install 1″ or 2″ rigid foam (depending on what my budget allows at the time) insulation to the 2×2’s creating a 1.5″ channel from soffit to ridge vent. The plan at the moment is to use 4′ pieces in each bay extending from just beyond the wall plate running up towards the ridge. I was thinking about changing the 4′ pieces to 8′ pieces and possibly running them all the way up to the continuous ridge vent. The roof truss stand at the wall plate is very small and after the 2×2’s and foam is in place may only be an inch or two…I was planning on blocking this off with another piece of rigid foam as well.
The second step is to make certain I have adequate/continuous soffit venting. I have aluminum soffits that were installed prior to my owning this place and I am almost certain they installed vented soffit panels but did not remove the old wood soffits they covered. I’ll take the aluminum soffit down and either remove the old wood soffit entirely or cut a continuous 12″ vent hole (overall soffit is 18″ in some places and 24″ in others).
The third step would be to add additional attic insulation in hopes of attaining R-38 or better. The attic is currently insulated with the original R-11(?) in the truss/ceiling joist bays and has additional R-25 roll insulation added to that. That total is close to R-38 and the roll insulation is criss crossed up there so it is fairly adequate…so adding more insulation would be the final (and most likely a bit down the road) step.
I live in the Chicago suburbs so the climate is cold as ‘ell at times (now) and hotter than ‘ell at other times.
Any thoughts as to whether this is a sound plan or if I need minor or major adjustments before I get into it?
The only other thing I’ll add is that the rigid foam I plan on using is the Owens Corning pink board readily available at the big box stores. I was not planning on using anything foil faced. And would I possibly achieve the same end (eliminating ice damning) with a lesser thickness of foam…maybe 5/8″?
Thanks a great deal for any thoughts or suggestions.
Tom
Replies
I would make step two step one. Make step three step two. then forget step 1.
Make sure you have good venting from soffits to ridge.
Make sure you insulate your homes cieling well paying attention to the details and everything should be fine.
I dont see the need to also insulate the roof from the attic.
Incidentally---
What did the salmon say when it bumped into the concrete wall?
Dam! (no "n").
The forums won't let me edit my title...maybe I'll get lucky and a moderator will edit it for me....bah, good catch - no pun intended!
Ice dams are a sign that there is snow on the roof and the heat from your house is escaping and melting the snow. As the melted water travels down the roof, it hits the soffit area where there is no heat escaping. The water freezes and then starts to back up under the shingles. You only see ice dams where there is heat in the building and snow on the roof.
The best solution for ice dams is to stop the heat from escaping. You can't stop all of it, that's why continuous ridge and soffit vents are used. They allow enough air to pass so that the attic stays cold. We have long, cold, snowy, winters in Maine. The minimum R-factor we look for is R-38 in ceilings.
At the eaves of the house, where the rafters/trusses sit on the outside wall, thick insulation will close off the air flow from the soffits. We use a product called PropaVent. Similar to what you want to do with the foam and 2x2s. These are styrofoam pans that staple to the underside of the roof sheathing between the rafters. You just need to make sure the air can get by, over the insulation, do not run them all the way to the ridge.
Insulating your attic will bring returns in your energy bill. Right now, you are heating Chicago. It will also quiet the house noticeably and help with cooling bills in the summer. The R-11 you have now, isn't doing very much. Installing two crossed layers of 6" unfaced fiberglass batts in your attic is an easy DIY project. You have to watch where you are walking and do a neat and thorough job. You can't insulate tight to certain types of ceiling light boxes.
There are advocates of using other insulation products. Some of these are not DIY friendly. Some may out perform fiberglass batts but some can have complications in a retrofit situation. The product you choose will often depend on price but the important thing is to stop your heat loss. Your investment will pay dividends.
Thanks for the replies.I do have additional insulation, by that I do not mean kraft faced batts. It's roughly a 10" diameter roll/tube shape about 25' long of what looks like fiberglass insulation encapsulated in what seems to be a 'homeowner friendly' type plastic bag (OC product I think, it's pink). Similar insulation I've seen in stores has been R-25. I know that is a bad description but I can't find a link to the product anywhere.I think if I add insulation it would most likely be blown in cellulose (because of cost and it doesn't itch) which I'd do myself. I'd go the route of blown in over batts to get better resistance to air leakage. I'm kind of uncertain if it'd be advisable to blow it in over the rolls off insulation up there so I'd have to look into that. But I'd rely on the matted down blown in cellulose to restrict air leakage from the ceiling because I can't really see the vulnerable areas due to existing fiberglass insulation and the roof being a 4/12 doesn't leave much headroom by the eaves.Other pricier alternatives like Icynene and what-not I'm not considering.
The r-38 is pretty good. You mentioned the soffit may not be vented but you should confirm before you remove it. He may have drilled holes in it between every bay. That would have been a good way to leave the old wood but allow the new soffit he installed to breath. Look in the middle of the day when the sun is out, look inseveral areas to make sure. It might be hard to get a look down in there but its well worth the effort. Is the insulation allowing the soffits to breath? You may just want to add one 4' section of rafter mate as mentioned to each bay just so the soffit can breath over the insulation into the attic. "Rafter mate" is the best way. The 1x2's will cost you more time and money. The Idea is to heat below the ceiling and lock it in below . Pay close attention around every pipe and wire. Once heat gets to the attic let it get out nice and fast so every thing stays dry and cool. Another fix would be to install a powerd attic vent ( in the gable or the roof). It will save you money . Combined with the ridge vent and soffit vent it would be more than enough even if he only drilled every other bay instead of every one. All you need is "draw and pull " , " air flow " to do a good job.
Also adding the blown in on top of the batts would compress them making them less effective. Fix what you have before adding and then see how things are. Remember the ice and water shield you installed is doing its job and protecting , no need to rush.
Edited 2/16/2007 12:22 pm ET by AllTrade
Edited 2/16/2007 12:25 pm ET by AllTrade
Edited 2/16/2007 12:38 pm ET by AllTrade
I appreciate the thoughtful response, thanks.I'm going to check on the soffits and whether or not they are vented this spring. I'm almost certain they are not. That will address attic ventilation issues but not solve my air leakage problem which is I'm sure the root cause of the ice damning. Any fix short of stopping the air leakage is just a band aid fix so to speak.That was my thought process for running a roof mate vent (although I was using thicker foam) 4' or maybe even 8' up the rafter bay....I figure I have leakage issues that I'll have some difficulty repairing and the extra 4' of rafter vent will get the warm attic air that much closer to the ridge vent before it hits the roof deck and melts the snow (which is also why running it all the way to the ridge vent was a consideration).For the cellulose, may I'll have to pull the R-25 rolls out of the way prior to blowing it in, then move the rolls back over the top of the cellulose. If the cellulose compresses the R-11 in the joist bays, so be it. R-11 in an attic space is pretty ridiculous anyway. I guess much thought wasn't given to energy conservation 40 something years ago.