Inspecting Your Homes Roof

A roof inspection is a through inspection of all roofing components, which include; roof vents, soffit vents, fascia, gutters, roof flashings and valley flashings, rafters or trusses, insulation, sheathing and the number of layers of shingles.

Roofs Structure

The roof over your head provides more than just shelter, it’s part of your homes support structure. Your roof provides protection against  rain, wind and snow and protects the rest of your house.  Your roof is also part of the attic ventilation system allowing air to circulate and prevent moisture buildup.  On the exterior of the roof the inspector will look for uneven roof planes and signs of sagging, which maybe caused by poor installation or roof component failure.

Roof Trusses

A timber roof truss is a structural framework of timbers designed to bridge the space above a room and to provide support for a roof. Trusses usually occur at regular intervals, linked by longitudinal timbers such as purlins. The space between each truss is known as a bay.  A roof truss is cross-braced into a stable, rigid unit. Ideally, it balances all of the lateral forces against one another, and thrusts only directly downwards on the supporting walls. 

One benefit of building with trusses is that you typically will eliminate interior support walls, as trusses are supported on both exterior walls.  This is a real bonus for home buyers who want to modify a homes layout to generalte a more open concept.


A rafter is one of a series of sloped structural members such as wooden beams that extend from the ridge or hip to the wall plate, downslope perimeter or eave, and that are designed to support the roof shingles, roof deck and its associated loads

Rafters have a tendency to flatten under gravity, thrusting outwards on the walls. For larger spans and thinner walls, this can topple the walls. Pairs of opposing rafters were thus initially tied together by a horizontal tie beam, to form coupled rafters. But such roofs were structurally weak, and lacking any longitudinal support, they were prone to racking, a collapse resulting from horizontal movement.

Rafters also require supporting interior walls, this sometimes is inconvenient for home buyers wanting to remove walls.

Inspecting Trusses

Mould can affect the integrity of your roof truss.  Un-treated mould on your roof truss will eventually rot the wood requiring replacement of the truss.Mould on roof truss

Damage can occur to trusses before they are even installed.  Banding applied to tightly during shipping can damage truss edges.   Improper handling during installation can cause extreme bending and damage to the connector plates. ( spreader bars are required to lift long truss members )

Gable end trusses are typically designed to be supported on end walls.  Some installers will mistakenly install these as clear-span members.

Connector plates will sometimes come loose and allow separation of truss joints.  The recommended number of nails must be applied as per installation instructions.  ( many building inspectors do not climb ladders so proper installation of roof trusses is never confirmed )

Attic Ventilation

Your attic shuld have sufficient ventilation that will allow equal levels of incoming and outgoing air. Ventilation should be placed in a way that allows air to enter from along the eaves and exit through the roof’s peak. In order to facilitate this exchange of warm and cool air, the general rule of thumb is to install at least 1 square foot of vent for every 300 square feet of attic floor.   

Poor attic ventilation is one of the major causes of ice dams on the eave of your roof.  Ice dams will damage your shingles and eventually cause roof leaks into home.

Ridge vents are very popular on custom homes as they operate at the highest point of your attic and are virtually hidden from view.  Turbines used to be very popular but in truth they will allow both snowSoffit-View-in-Attic and water into your attic and most professional roofers no longer install them.

Soffit vents can become blocked by poor insulation installation practices.  Wood soffit venting has a small opening to start with so when you inadvertantly fill or partially fill the opening with blown insulation you may soon develop a moisture problem in your attic.

Ideally your attic temperature should be relatively close to the outside air temperature.   Good ventilation is imperative for to prevent build up of heat or excessive moisture in the attic area.   Even a simple thing as not having a proper seal on your attic access hatch will often cause mould to occur on the access wood structure.

One cheap homemade mould removal product is vinegar and water.  Simply mix the two products in a spray bottle and spray the affected area.  Let sit for one hour and wipe with damp cloth.

Roof Sheathing

Sheathing, also known as decking, serves as the bed for the other components seen on residential roofing systems. During a roof replacement, it is one of the things that we have to make sure it is in good shape, as the roof’s long-term performance depends on it.  Roofing panels are manufactured with fully waterproof adhesive.  They include plywood, oriented stand board (OSB), and composite panels made up of a combination of wood veneers and reconstructed wood layers. Plywood panels are manufactured by gluing together three or more cross-laminated wood layers. OSB panels are made from multiple layers of wood flakes oriented 90 degrees to each other. Sheathing provides the base for attaching the roof covering and adds strength to the framed structure.

Areas of weakness can result in serious deflection, unusual bounciness and movement in the deck, corrosion of steel deck surfaces or rotted wood planks.

Note whether plywood sheathing meets construction grade under the applicable CSA standards.

  • CSA Standard 0121 Douglas Fir Plywood
  • CSA Standard 0151 Canadian Softwood Plywood
  • CSA Standard 0153 Poplar Plywood
  • CSA Standard 0325 Construction Sheathing

H- Clips Add to the Support

H-clips are important to add to the strength of the boards. Also known as panel-edge clips, they are made of steel and fit in between the wood panels to keep the edges from feeling soft or sponge-like. The benefit of the H-clips is they help evenly distribute the weight between the panels. They also help contractors save money as the clips make the boards more sturdy, thus requiring fewer materials.


The Orillia Home Inspector

For more information on Roof Inspections call Roger at 705-795-8255

Send Roger an Email   [email protected]

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