Steep Roofing

Roof Solid State Home Inspections

Our homes would not be warm and dry if not for the roof over our heads. For Home Inspectors, the roof is a critical system to look at during a home inspection as the roof not only keeps the home protected from the elements, but it also forms part of the main structure of the house.

Steep Roof Design

Steep roofs are the most common style for single family houses in western construction as they are easy to construct, shed water well, provide overhangs to protect walls, are easy to ventilate, and have a traditional appearance. 

Steep roofs are not necessarily 'steep'. For roofers, there are three primary roof slope types based on the rise and run of the roof system. 

  • Flat roofs are essentially flat except for slight slopes to direct water to drains
  • Low slope roofs are from 'flat' up to a slope of 4:12 (e.g. 4" vertical rise per 12" of horizontal run)
  • Steep roof systems are anything over 4:12 or at least an 18.43 degree angle

The roof itself is a major part of the homes structural system. It provides bracing to hold the walls vertical as well as carrying the loads of snow, rain water, and roofing materials from above. Roof design and structure is critical to roof performance and there are two primary roof structural systems for steep roofs:

Rafter and Joist Construction

Until the mid 60's, it was common for builders to make site-built rafter and joist systems as the structural 'bones' of the roof system. Rafters are the angled wood pieces that run from the outside walls to the peak of the roof. Joists are horizontal wood that connects the wall ends of opposing rafters to each other. The three points of connection (wall, opposing wall, roof peak) form a structural triangle which is one of the strongest shapes for carrying a load. Additional collar ties, purlins, and knee walls could be added by builders to increase load strength and horizontal spanning distances.

Site-built rafters were typically very functional but they had a few down sides for home owners. First, they are only as good as the builders skill is at making them and structural failure or high snow loads in some climates would cause home owners to need to re-enforce weak rafters. Second, rafters limited house designs to simple roof shapes that could be built with the traditional skills and construction load tables of on-site labourers.

Engineered Truss Construction

Roof Truss Solid State home Inspections
Wooden roof trusses stacked together on a building site

Starting in the late 60's, it became common to order factory built engineered trusses for new construction. Engineered trusses are custom built for each home based on home drawings sent to the truss manufacturer with the goal to maximize strength and minimize material costs. A common way to recognize engineered trusses is the use of metal connector plates installed by the factory at the wood piece junctions. Site-built rafters would be nailed together.

Engineered trusses can be made much stronger than site built rafters using more complicated angles and additional 'web' supports. With engineered trusses, builders and architects could also begin to design more complicated home designs along with larger open spaces which radically changed the design of homes in the later half of the 1900's.

Steep Roof Cover Materials

Once the structural bones of the roof are in place. Roof coverings are needed to provide weatherproofing to the home below.

  • Asphalt Shingles - Ahphalt shingles are the most common roof covering on single family homes. First, a plywood 'deck' is built on the roof trusses, then an underlay of tar felt or plastic for waterproofing, and finally overlapping of shingles are laid. Shingle roof systems are not waterproof but instead each shingle acts as an umbrella rolling water off to the next shingle in the system until the water sheds from the roof. Asphalt shingles are economical to install, come in many colours, and can last 20-30 years based on the warranty of the manufacturer and installation quality.
  • Wood Shingles/Shakes - Cedar wood roof systems have been around for centuries but were very popular in the 90's in some areas. Rather than using a plywood base deck, wood shingles would be installed on 1/4 strapping attached to the trusses with gaps about 8-10" apart with a tar paper underlay. Wood shingles can last 20-30 years but in wet climates, they may prematurely fail if they cannot dry regularly. Wood is similar in price to asphalt shingles however there are many grades of quality that can effect the pricing.
  • Tile - Tile roof systems can be made from clay (like spanish style designs), cement, slate, metal, or many other materials. The installation of each system is can be very different however tile systems tend to be premium systems with longer life spans than wood or asphalt shingles. Unfortunately, they are also more expensive to initially install.
  • Sheet Metal - Metal Roofing systems installed in sheets are rarely seen on single family homes unless they are in a high snowfall area like mountain resorts or used for architectural statements. Metal roof systems last a similar timeline to asphalt and wood shingles however they tend to be noisier in rains. Failure of sheet metal roof systems tends to be at the attachments as they need to be screwed into the face of the metal which can eventually allow water to leak in and cause rust holes.
  • Roll Roofing - There is a roll roofing asphalt product available that can be installed on flat roofs very economically. It however has a very short life span at no more than 5 years. It is rare to see this roof product installed on single family houses but it can be seen occasionally as a short term roof solution.

Steep Roof Flashings

A primary roll of our roof is to shed rain and snow water away. Ideally, roofs would have an uninterrupted cover material from peak to edges but this is typically not possible as chimneys, skylights, plumbing vents, electrical masts, walls, and other house elements come into contact with the roof system.

In order to direct water safety to the roof edges around penetrations, flashings are used around each of these roof obstructions. The principle of flashings is quite simple in that it should direct water away down the roof slope and not have any opportunity for water to get behind the flashing. The practice of installing flashings however is much more difficult. Working with masonry chimneys or walls for examples requires a waterproof connection to masonry which is difficult and time consuming to accomplish which is why it is often done very poorly. Another common flashing defect found in home inspections is a missing 'cricket' which is a large sloped flashing for roof penetrations wider than 30" such as a chimney.

As most roof coverings can last 20 or more years, it is important that roof flashings be all replaced at each roof system replacement. Expecting thin metal flashings to last exposed to the elements 40-50 years spanning to a third roof replacement cycle greatly increases the risks of roof leaks in the future.

Steep Roof Inspection Safety

Roof inspections can be the most dangerous part of a home inspectors job. Home inspectors typically work alone which means nobody is around to call for help in an accident and there are no code requirements to provide safe areas for roof inspections. Home inspection professional standards allow the home inspector to make the call on whether accessing a roof is safe or not. If the roof is too steep, too slippery, made of fragile materials, or no safe ladder access is available, it only makes safety sense for the inspector to view the roof from ground level with binoculars. This does however limit an inspectors ability to give a full roof assessment.

What Home Inspectors Look for on Steep Roofs?

Home inspectors will be looking for many issues on steep roofs including:

  • Structure - Are there any signs of sagging, splaying, or other indications of roof structure failure
  • Covering - What is the type and general condition of the covering? Is maintenance or replacement needed?
  • Flashings - Are the correct flashings in place and is any maintenance needed
  • Chimneys - Describe the chimney systems and determine if any maintenance or further evaluation is needed
  • Skylights - Check to see they are secured, flashed, and not showing signs of condensation or failure
  • Plumbing Vents - Ensure they are secure and free of obstructiuons
  • Roof Ventilation - Make a general assessment of the quantity and quality of roof ventilation

Final Thoughts

Roof systems are very complicated areas of the home but fortunately well installed materials should give home owners decades of nearly maintenance free use. Unfortunately, roof systems are one of the most expensive home systems to replace which makes understanding the quality and condition of a roof very important for home owners who may need to budget for replacement. 

Always call in a professional home inspector who will assess your roof and other major home systems if you are considering buying a new home. Knowing your homes systems will give you the best advantage when it comes to keeping your home and family safe and solid.

By James Bell - Owner/Operator of Solid State Inspections Inc.