Ice barrier underlayment is a layer laid under the covering at the eave and in the valleys, to keep meltwater that gets under the shingles from entering the house. Ferry County requires it, and this guide explains what the layer does, where it goes and what it does not do.
Key takeaways
- The layer keeps meltwater out of the house where it gets under the shingles at the eave.
- Ferry County requires ice barrier underlayment, and it is part of every re-roof here.
- The layer is laid from the eave up the roof, with its own strip in the valleys.
- The layer does not replace ventilation, insulation or the frame check.
The problem the layer solves
At the eave, meltwater can run under the shingles and freeze, and the layer stops it reaching the deck.
A snowy roof melts from below as the attic warms, and the meltwater runs down the deck to the eave. At the eave the water meets the cold, freezes and builds a ridge. The water then backs up under the shingles and finds the nail holes, the joints and the edge of the deck. A plain covering does not stop that water, and once it is under the shingles it can run into the wall, the ceiling and the insulation.
The ice barrier is a continuous sheet that sits under the covering at the place where the water is most likely to back up. It does not stop the ice from forming. It stops the water that gets past the ice from reaching the house.
- Meltwater runs to the cold eave
- Water backs up under the shingles
- The layer stops water reaching the deck
Where the layer goes
The layer runs from the eave up the roof, a set distance past the warm wall line, and it has its own strip in every valley.
The layer starts at the eave edge and runs up the roof past the line where the warm wall of the house sits inside the attic. That line is where the snow melts most, so it is where the layer has to be. The exact distance up the roof is set by the county rules, and the crew checks the rule for the specific roof before it lays the layer.
In each valley the layer needs its own strip, laid so the water runs down the valley and not across it. A valley with no strip, or a strip laid against the flow, is a line of leaks in the first thaw.
- Starts at the eave edge
- Runs past the warm wall line
- Own strip in every valley
How the layer is laid
Each course overlaps the one below, so the water sheds toward the eave and out.
Each course of the layer overlaps the course below it, so that water running down the roof passes over the joint and not under it. The overlap is laid in the direction of the water flow, which means the upper course always lies over the lower one. A course laid the wrong way creates a channel for the water to run into.
The nails are placed where the next course will cover their heads, and the fixing is set so the layer lies flat without wrinkles. A wrinkle in the layer is a point where water can collect and freeze.
- Each course overlaps the one below
- Upper course lies over the lower
- Nails placed where the next course covers them
Penetrations, valleys and the flashing
Pipes, vents and the wall flashing are the points where the layer must be cut and sealed.
Where a pipe or vent passes through the roof, the layer is cut around the flange and sealed so no gap is left between the layer and the pipe. The flashing at the wall line is laid over the layer, with the layer tucked under the flashing so water runs over the join.
A gap at any of these points is where the meltwater will find the deck first, and the crew checks each one on a re-roof before the covering goes on.
- Pipes and vents cut and sealed
- Wall flashing laid over the layer
- Each penetration checked before covering
What the layer does not do
The layer is one part of the protection, and it does not replace the other parts.
The layer does not stop warm air from the house rising into the attic and melting the snow from below. That is a question for the ventilation and the insulation, and the crew checks both on the same visit. A roof with a perfect layer and a warm attic will still form dams at the eave, and the water will still find a way past the layer where the layer is thin.
The layer also does not carry the snow. The frame is checked against the county snow minimum separately, and a sagging frame is not repaired by adding a layer.
- Not a substitute for ventilation
- Not a substitute for insulation
- Not a substitute for the frame check
Checking a layer before the covering goes on
A layer is checked before the covering is laid, because afterwards it cannot be seen.
Before the covering goes on, the crew walks the layer and checks the overlaps, the valley strips, the penetrations and the nail line. Any wrinkle, gap or loose nail is corrected at that stage. The check is recorded with photographs, because the layer is hidden once the covering is laid.
The owner can ask to see the layer before the covering is laid. A crew that is confident in its work will show it, and the photographs in the record are the proof for later.
- Overlaps and valleys walked before covering
- Wrinkles and loose nails corrected
- Photographs kept as proof
Questions to ask about the layer
Ask where the layer runs, how far up the roof it goes, and what the valleys have.
Ask the crew to show you the eave line on the scope, the distance up the roof the layer will run, and the valley strip. Ask how the penetrations are sealed and whether the layer is shown in the photographs. A scope that does not mention the layer at all is a scope to question.
The answers are kept with the scope and the record. A re-roof in Ferry County should carry the layer, and the record should show it.
- Eave line and distance shown
- Valley strip stated
- Layer shown in the photographs
Ice barrier and the warm attic
The layer and the attic work together: the layer catches the water, and the attic stops the melt.
The layer is the last defence at the eave, not the first. The first defence is an attic that stays close to the outside air, so the snow on the roof does not melt from below. Insulation at the outside wall and clear soffit vents that let cold air move under the deck are the two measures that keep the snow in place. A warm attic will overwhelm any layer over time, because each melt cycle pushes more water to the eave.
The crew checks the attic temperature and the insulation at the eave on the same visit as the layer. A finding in the attic is recorded with the layer finding, so the owner sees the whole problem and the whole fix.
- Attic kept close to outside air
- Insulation at the outside wall checked
- Attic and layer checked on one visit
Materials and the sealed laps
The layer is a material that must stay sealed at its laps and its edges.
The layer is laid with its laps sealed where the material requires it, and the edges are fixed so they cannot lift in the wind. An unsealed lap or a lifted edge gives the water a route under the sheet. The owner can ask what material is used and how its laps are sealed, and the crew records the answer.
Heat from the sun can change how the material lies on a roof in summer, so the crew checks the layer again after the first hot season on a new roof where that is practical.
- Laps sealed as the material requires
- Edges fixed against wind lift
- Layer checked after the first hot season
A re-roof on an old layer
A re-roof over an old layer is a different job from a new deck, and the old layer must be read before the new one goes on.
Where the old covering is removed, the old layer is removed with it and the deck is read. Where a new covering is laid over an old one, the old layer may not lie flat or may hide a soft deck, and that is a reason to remove the covering rather than lay over it.
The crew reads the old layer when the covering is off. A layer that is torn, short or laid the wrong way is replaced, and the record shows what was there and what replaced it.
- Old covering removed where needed
- Old layer read when the covering is off
- Replacement recorded against what was found
Ice barrier on a metal roof
A metal roof sheds snow differently, but the eave and the valleys still need the layer below the panels.
Metal panels shed water over their profile, but the water that gets under a panel at the eave needs the same layer as a shingle roof. The layer is laid under the panels at the eave and in the valleys, and the panel fixings must not pierce it in a way that leaves a gap. The crew checks the penetrations at each fixing on a metal roof.
Snow sliding off a metal roof loads the eave in a different way, and the layer is checked after any sliding snow that has bent the first panels.
- Layer under panels at eave and valleys
- Fixings checked for gaps in the layer
- Layer checked after sliding snow
Frequently asked questions
Is ice barrier the same as the underlayment on the whole roof?
No. The ice barrier is the layer at the eave and in the valleys, and the rest of the roof may have a different underlayment. The scope should name both.
Does the layer stop ice dams?
It stops the water that gets under the shingles from reaching the house. It does not stop the ice from forming, and the attic warmth has to be checked as well.
Can I add the layer to an existing roof?
Usually it is laid during a re-roof, when the covering is off. A repair can sometimes add a section at the eave, and the crew says whether that is practical for the roof.
Who checks that the county requirement is met?
The owner can ask the crew to show the layer in the photographs. The county office administers building applications, and a question about the requirement for a specific job can be put to that office.
Sources
This guide is general information for Ferry County homeowners, not a substitute for an on-site inspection. Prices are estimates. See our disclaimer.