Roofing
The roof serves as your home’s primary barrier to rain and snow - keeping water out of your home is particularly important during construction. Water is an enemy of most construction materials and trapped moisture can encourage growth of mold.
If possible plan for any future penetrations through the roof prior to installing or repairing an existing roof. It is always more work and less effective to retrofit penetrations through an existing shingle or membrane roofing installation. Some examples of potential penetrations include chimneys, flues, roof vents, plumbing stacks, and skylights.
Roof Types
There are three primary types of roofing found on homes in Des Moines: single-ply membrane (flat), built-up (flat), and the most common being shingle/tile (sloped). Some buildings have combination roofs with a sloped roof in front and a flat roof in the back.
Built-up roofing (BUR) is a generic term for any roof that is built with multiple layers on a flat roof. A BUR system typically has layers of “felt” or other membrane alternated with layers of tar/bitumen. The top layer is usually a stone aggregate spread over the entire surface. This roofing type is more typically found on commercial buildings.
A single-ply membrane (SPM) roofing system consists of a single layer of waterproof sheeting. The SPM material comes in large rolls, and can be fastened in a number of ways to the substrate on a flat roof. Its ease of installation makes SPM systems relatively inexpensive.
Asphalt shingles are the most common roofing system on sloped roofs. Shingles are mechanically fastened (nailed) to the roof’s substrate. A layer of roofing felt between the shingles and the substrate helps provide a waterproof barrier. In general, shingles may be installed over existing shingles up to three layers deep. All layers must be removed prior to the subsequent installation - this is also a good time to make any required repairs to the roof sheathing. If your building has existing slate shingles that cannot be repaired, they should be removed before installing asphalt shingles.
Insulation
Roof rafters and trusses must be insulated to prevent heat loss in the winter and heat gain in the hot Iowa summers. In fact, the roof is one of the primary means of heat transfer to and from your home. The two most common means of insulating the roof are fiberglass batts and blown insulation. Fiberglass batts come in either large rolls or pre-cut lengths that are placed between rafters or studs. Batts are typically installed before drywall and after electric rough-in. Blown insulation consists of fibers (often recycled material) and a fire retarder. It is spread evenly using a blower that may be rented. It is important to use enough to get the required thickness for the desired insulation value.
Resistance to heat flow is indicated with an “R-value”. The higher this number, the more insulation is provided. Insulating the roof to as much as possible will result in significant energy savings.
In some cases, if the underside of the roof sheathing is exposed, it is possible to install expanding foam insulation such as Icynene. This type of insulation is very efficient (high R-value) and serves double duty as a vapor barrier but requires professional installation.
heat tape
Would this help to prevent the ice dams? I see this on a few houses near the edge of the roof, so I assume it keeps the snow and ice to build up. Anyone have any experience with this?
Thanks Susan
Metal Roof
We had a metal roof put on our house from bakeris roofing.. looks nice and will last longer than I will. They put in a power fan with a humidistat. It pulls air through the roof vents to keep the humidity down, so it sounds a bit strange walking by and hearing the roof fan on in this wonderful weather. They also put in some additional vents along the hip of the roof as well. Now that attic has insulation on the floor but basically it is just there, no real access or desire to go up there anyway.
When they put the roof up there, they did put the vapor barrier and the usual stuff, but this is metal and they also fixed that so hopefully with the ice dams it won’t wick under. I have some interesting icsicles out there. It seems that the warm days we did have , the ice went that way.
It looks like it is going to be cold through next Sunday. I have a Davis weather station and I put in the attic a probe that tells me the temperature and humidity… it is 39F and 73% humidity. The fan will kick in when the humidity gets to 80%.
Ice Dams
That is an excellent question... for those of you who are reading this and aren't familiar with "ice dams", they occur when water works its way back up under shingles via the freeze/thaw cycle. When the ice and snow on your roof melt, it resulting water can defeat the shingle system and find its way into the interior of a building.
The most common cause of ice dams is an inadequate roof insulation and air sealing. Believe it or not, you actually want a cold roof surface in winter! When warm air from your house warms the bottom of your roof surface, the bottom layer of snow melts and runs down the roof surface (as it is supposed to). However, when it reaches the uninsulated eaves where there is not warm air from your house heating the roof, the water refreezes.
The refrozen water causes two main problems. First, when water freezes (the "ice" part of the ice dam), it expands. This expansion can lift your shingles and push your gutters and soffits away from your house. Second, the "dam" part of an ice dam creates a barrier that prevents water from draining. The melting water from the warm roof above is held in a pond against the shingles, which are not intended to serve as a pool liner. The resulting water can then leak into the roof cavity and into the structure below.
Short term solution would be to chip-chip-chip. I don't know of any other way to deal with existing ice dams, other than to perhaps close off all heat to your attic area and see if that can keep the roof surface cool enough to prevent new ice dams from forming.
The long term solution, of course, is to rework the insulation system to allow for adequate ventilation above the insulation in your rafter system. The cold air needs a path from the soffit all the way through to the ridge of your roof (typically at least 2") in order to provide enough circulation to keep the roof surface cold enough to prevent ice dams. There are several products one can install that create a standoff distance between the fiberglass insulation and the roof sheathing.
The problem: in many older homes, the rafters are 2x4. This is not enough space install fiberglass insulation with an adequate air space for ventilation. In this case, there are two options: fully insulating the cavity with spray foam insulation and furring out the rafters to create more space within the rafter system. Both options are probably quite spendy. I don't have enough specific experience with spray foam insulation to say definitively whether it will solve an ice dam problem.
Typically, and I believe required by code nowadays, an ice and water shield is installed below the bottom three feet of shingles on a new shingle installation. This barrier is essentially the same as a pool liner that provides an extra barrier to prevent water from infiltrating the roof system. It is not a solution for the primary causes of ice dams, just an extra layer of protection for once they form.
I'm working on a page for RenovateDSM that details how to air-seal and insulate behind the wing walls of a finished attic space.
Spray Foam Insulation
Spray foam is not necessarily a good idea if moisture gets trapped between wood that is surrounded by spray foam. If wood gets wet and can not dry out it rots and then eventually fails. Installing foam in walls of historic houses is also not recommended because moisture can be trapped and rot with sill or any horizontal surface. To avoid moisture being trapped in an insulated wall it is absolutely imperative to establish a vapor barrier on the inside (warm) wall. That means painting a vapor barrier on the wall or if the plaster is gone, installing a vapor barrier before installing plaster board.
Ice Dam
So now I've joined the ranks of DSM homeowner to have ice dams. I have lost my brother-in-law labor force who chipped off the ice dams over Christmas and now the ice dams are back. I'm dreading the warm-up and the resulting flood inside my house. Any ideas on what to do to either prevent the impending flood and to prevent ice dams from forming?
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