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We are planning on having standing seam metal roofs installed on our log home and log barn each with gambrel roofs. The house has a roof over the entire porch. There is one layer of 3-tab shingles on each roof which are twenty-one years old. We have ventilation on each end of the peaks of the roofs. We have no soffit ventilation and our concern is ice dams occurring at the joints of the two pitches of the roofs where we presently have roofing wires. The contractor, who we choose from your site, recommends removing the shingles because he said that ripples can occur on the metal roofs. He also recommends installing Grace Ice & Water Shield self-adhered Roofing Underlayment. Is this the recommended procedure? Also, how do chimney sweeps clean the chimney which is in the middle of the roof? Will there be damage to the metal roof? Is power-washing done from the sides of the roofs so as to avoid injury?
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Lets look at why your existing roof failed and from what you said, there is no soffitt ventilation or ridge ventilation but there is gable ventilation in eack end near the peak. Assuming that you have an attic, then this ventilation is totally inadequate as the gable vents will only remove air at the top 1/3 of the attic space at best. Coupled with this you probably also have some heat loss unless the ceiling has monolithic air barrier and the snow melts on the top and runs down and frezes over the prch and creates an ice damm. If you haver some vaulted ceilings near the eave then it makes the situation worse.
Now is your chance to fix it right. First is ask to see the product approval report on the metal roof system you choose which will show that it has been tested and how to install it to meet the building codes. If you have choosen a smooth finish, then you willget more snow avalanching and it may add to your problems at the junction unless you ventilate.
I would suggest choosing a system that sits up off the deck on strapping. I would remove the existing shingles and inspect for damage. Then I would use the ice and water shield on the porch and up past the transition at least three feet and use a good quality underlayment for the balance. Then have the roof strapped vertically over the existing rafters with 1 1/2" material and fastened into the rafters. This will allow for vertical air flow and if any damming does happen it can readily self drain out. Make sure that the eaves has proper intake venting. This can be accomplished with vented closure strip and the same at the ridge. I would then open up the ridge to vent the attic and seal up the existing gable vents however I would install some new ones on the gables down at the ceiling level for intake.
As to the roof access. In that area, it is possible to put some support under a certain sheet such as ridgid insulation to support walking and have a roof anchor installed at the top for the seeps to rope off to. Hope this helps.
3/3/2005
Dura-Loc Roofing Systems, Inc.
3/4/2005