Ferry County sets a minimum roof snow load of 40 pounds per square foot countywide, and suggests 55 pounds per square foot or more at elevations of 3,000 feet and above. The figure is for the roof, not the ground, and it is the reference the frame is checked against.
Key takeaways
- The county figure is a roof load, not a ground load.
- The 40 psf minimum applies countywide, and 55 psf or more is suggested at 3,000 feet and above.
- A frame that was built to a lighter standard may need strengthening before a re-roof.
- The ground snow figure for individual towns was not published in the sources for this site.
Roof load and ground load are different
The county figure is the load the roof must carry, and it is not the depth of snow on the ground.
A roof snow load is the weight of snow the roof is designed to carry, measured in pounds per square foot. The ground snow depth is a different number, and the two are related through the roof shape, the exposure and the way the snow settles. A house on a ridge can carry more snow on the roof than the ground depth alone would suggest, because the wind pushes the snow to the lee side.
The county figure is therefore the starting point for a roof check, not a measure of how much snow is on a particular roof. The crew reads the attic and the frame against the figure, and it notes the exposure of each roof.
- Roof load is a design load in pounds per square foot
- Ground depth is a different number
- Exposure changes the load on a roof
The countywide minimum
The 40 psf minimum is the floor the county sets for every roof in Ferry County.
Ferry County building rules set a minimum roof snow load of 40 pounds per square foot. A roof that is designed to a lower figure does not meet the county minimum, and a re-roof on that frame must be checked and, if needed, strengthened to the county figure.
The minimum applies across the county, so a roof in a valley town and a roof on a high bench are both measured against it. The higher figure for elevation applies on top of the minimum where it is set.
- 40 psf is the countywide minimum
- Lower-designed frames must be checked
- Applies in valley and high towns alike
The higher figure at elevation
The county suggests 55 psf or more at 3,000 feet and above, and the crew uses it where the elevation applies.
The Ferry County figures suggest 55 pounds per square foot or more at elevations of 3,000 feet and above. A house at that height or above is read against the higher suggested figure, and the crew states on the record which figure it used and why.
The elevation of a house is read from the site, not from the nearest town. A house on a bench can be well above a town whose name it shares, and the crew checks the actual elevation before it chooses the figure.
- 55 psf or more suggested at 3,000 ft and up
- Elevation read from the site
- Figure used stated on the record
What the frame check looks at
The frame check looks at the rafters, the ridge, the bracing and the wall plate against the load.
In the attic the crew reads the rafter size and spacing, the ridge board, the collar ties and any bracing. It checks whether the frame shows a sag, a cracked joint or a brace that has moved. A frame that shows any of those is read against the county figure and marked for strengthening if the figure is not met.
The readings are written at fixed points so the next visit can compare the same spots. A frame that has been checked once and recorded is much easier to read the next winter.
- Rafter size and spacing recorded
- Sag, cracks and moved braces noted
- Readings taken at fixed points
What the owner should ask
The owner should ask which figure the crew used, why, and where the frame stands against it.
Ask the crew to state the county figure it used for your roof, the elevation it read, and the result of the frame check. A written answer to those three questions shows that the check was made to the county rule, not to a general assumption.
If the crew says the frame needs strengthening, ask for the work to be listed as its own line in the scope, with the readings that support it. That line is the proof of the work if the roof is later looked at.
- Figure used stated in writing
- Elevation and result recorded
- Strengthening listed as its own line
Where the figure does not reach
The sources for this site do not give ground snow figures for each town, and this guide does not invent them.
The county page gives the roof minimum and the elevation suggestion. It does not give a separate ground snow load for each town, and the sources for this site do not provide one. Where a house sits in a place the sources do not describe, the crew reads the roof against the county figure and says that the town figure was not used.
That is an honest limit. It means the frame check is made to the county rule, and any finer figure for a particular site would need a separate source.
- Town ground figures not in the sources
- County roof figure used instead
- Limit stated on the record
How the load goes from the roof to the walls
The snow load travels from the covering to the deck, from the deck to the rafters, and from the rafters to the walls and the ground.
The load starts on the covering and passes to the deck boards or panels, which carry it to the rafters. The rafters pass the load to the ridge, the wall plate and the ceiling joists, and from the walls to the foundation. A weakness at any point in that path changes how the roof behaves. A soft deck spans too far between rafters, a rafter with a cracked joint loses its capacity, and a wall plate that has rotted gives way at the eave.
The crew reads the path from the top down and from the bottom up. The attic shows the rafters and the joints, and the covering shows the deck. Each step is measured, because the county figure is only useful when the frame is read against it.
- Covering to deck to rafters
- Rafters to ridge, plate and joists
- Weakness at any point changes the load path
The eave and the snow that slides
Snow that slides off a roof lands on the eave, the gutter and the ground below, and the eave must be read for that.
A roof that sheds its snow onto the eave can drop a slab of snow in one piece. The slab loads the gutter, the brackets and the fascia, and the impact can bend the first panels or pull the eave trim. The eave is therefore read for the slide as well as for the static load.
Snow guards are the usual repair where the slide is a repeated problem. They hold the snow on the roof so it melts in place. Their layout is set by the pitch and the path of the slide, and the crew records the layout on the scope.
- Slabs load the gutter and fascia
- Eave read for slide and static load
- Snow guards set by pitch and slide path
Frame strengthening and what it involves
Strengthening a frame is a structural job, and it is recorded as its own item.
Strengthening is done by sistering a rafter, adding a brace, fitting a purlin or setting a new ridge board, depending on what the readings show. Each is a defined piece of work with its own fixing, and each should be on the scope as a line item with the reason for it.
The work changes the load path, so it is checked after it is done. The crew measures the sag again at the same fixed points and records the result. A strengthened frame that moves again after the next winter is a frame that needs a closer look.
- Sistering, bracing, purlin or ridge work
- Each item on its own line with its reason
- Re-measured after the work
Seasonal checks through the winter
A frame that holds through one winter may move in the next, so the checks are made each year.
After the first heavy snow, the owner can look at the eave and the ridge from the ground for any change. In the spring, the crew reads the attic for a new sag, a new crack or a wet insulation patch. The two checks are cheap compared with a frame repair, and they show the trend that a single reading cannot.
Keep the readings with the house file. A record of the ridge drop in one spring and the next gives the owner a clear view of whether the roof is holding.
- Ground look after heavy snow
- Spring attic read for new sag or crack
- Readings kept with the house file
What a snow failure looks like
A snow failure often shows first as a stuck door, a cracked ceiling or a sagging ridge, before any shingle has moved.
The first signs of a frame under too much load are often inside the house. A door that sticks at the top, a crack that runs along the line of the ceiling joists, or a wall that has started to bow at the top are all signs the load is moving. The crew asks the owner about these signs on the first call, because they point to the frame before the covering shows anything.
A failure that is still developing is easier and cheaper to correct than one that has already let the roof down. The owner should report the signs early and not wait for the spring.
- Stuck doors and ceiling cracks
- Bowing walls at the top
- Report signs early
The county figure and the house you own
The county figure is the same for every roof, but each house has its own frame, and the frame is what is read.
Two houses in the same county can have very different frames, because they were built at different times, to different standards and with different materials. The county figure is the test the crew applies to each one. A frame that passes the test is recorded as passing, and a frame that does not pass is recorded with the readings that show why.
The owner should not assume the frame meets the county figure because the house is newer. The check is what settles the question, and the record of the check is what the owner keeps.
- Same figure, different frames
- Each frame read and recorded
- Owner keeps the check, not an assumption
Frequently asked questions
Is 40 psf the snow on my roof?
No. It is the minimum roof load the county sets. The depth of snow on your roof is a different measure, and the crew reads the roof rather than assuming the depth.
Does my roof need 55 psf?
It depends on the elevation. The county suggests 55 psf or more at 3,000 feet and above. The crew checks the actual elevation of your house before it applies the figure.
Can a sagging roof be fixed by covering it?
Not usually. A sag is a frame issue, and a new covering laid over a sagging frame will show the sag again.
Is the county figure the same as the building permit?
No. The figure is a design rule. A permit is a separate question, and Ferry County Planning and Building administers the building applications.
Sources
This guide is general information for Ferry County homeowners, not a substitute for an on-site inspection. Prices are estimates. See our disclaimer.