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What Does It Mean if You Have a Sagging Roof?


When a roof has a curved or wavy appearance as opposed to a straight one, it often points towards a sagging problem. Sagging is a common roofing problem that appears in homes with roofs that haven’t been replaced in a long time due to a deteriorated structure.

They are also a common problem in older homes due to the way roofs used to be built.

If your roof’s ridge is starting to take the shape of a saddle, you might look on the bright side and consider it a “Western” décor detail. On the other hand, there are better ways to get a rustic look, and that roof is really more like an old swayback horse that needs special care.

The cause of a sagging roof is straightforward in theory: not enough structural support for the load. Solutions can range from simple to downright ugly (for your wallet), and unless you’re comfortable with span tables, advanced carpentry and working at heights, fixing a sagging roof is almost always time to call a pro.

Traditional sloped roofs rely on the strength of triangulation. If you glue three popsicle sticks together at their ends to form a triangle, you’ve got a decent model of how a roof frame works.

Holding the triangle upright, the angled sticks that meet at the top are the rafters; the horizontal stick at the bottom is the rafter tie. Rafter ties often double as ceiling joists for living space below the roof and attic floor frame members.

What Are the Causes of a Sagging Roof Line?

When’s the last time you took a good look at your roof? When the framing is done properly, the angles of your roof should be as straight as arrows. However, over time, it isn’t uncommon for roofs to sag or show other signs of distress. If this is the case, you’ll need to call an experienced Melbourne roofing company as soon as possible to reduce the risk of further roof damage or worse, your roof collapsing.

How To Fix A Sagging Roof

Water Damage

Roofs deal with a lot of runoff over time, which is why it’s important to see how rainwater drain from your roof. Water has a way of finding the imperfections in your roof where it can seep in and cause damage.

Over time, the trapped moisture creates the perfect environment for mould and mildew to grow, further weakening your roof and causing it to sag.

The structural integrity of your roof depends on being impervious to water damage. For this reason, we recommend having a licensed roofer come out to your house every three years even if you think your roof is fine, to inspect for water damage on your roof.

Inadequate Roof Joints and Rafters

Think of your roof as a triangle. The triangle base forms the ceiling or roof joints, while the rafters are the diagonal walls that slant toward the ridgeline. When the roof joints and rafters are improperly constructed, this can lead to a sagging roof later on.

The weight of your roof pushes down on the ridgeline before being distributed down through the rafters, roof joints, and walls of your home.

This design is meant to safely carry the load on top of your house, including the roof, shingles, snow, and ice.

However, when a residential roof isn’t built properly, it can cause the roof to sag over time and become structurally unstable. Top Glaze has the best range of help if you’re looking for Melbourne roof repairs.

Old Age

Most roofs start deteriorating once they reach the end of their lifespan.

When given proper roofing maintenance, roofs can easily last for more than a decade. However, once you notice your roof is beginning to sag, you need to call a licensed roofing company as soon as possible for a roof repair or restoration.

Some other causes of a sagging roof include lower-quality materials and a damaged or sinking foundation.

If you need help determining the cause of your sagging roof, please feel free to contact our team to schedule a free inspection.

6 Things to Check in the Attic

Check Rafters and Trusses

One of the most common causes of roof issues are problems related to the rafters or trusses; therefore, giving them a good look is critical when addressing sagging, bowed or wavy roofs.

They have issues for a wide variety of reasons, including damage from rain stroms, severe wind, leaks, etc.

In the attic, both rafters and trusses should be checked for cracks and damage.

If the review from the exterior or interior detected any warning signs, then especially check the areas in the attic that are near the warning signs observed.

Truss connector plates

When there is extreme stress or overly heavy loads on a truss, the nailer/connection plates may come loose or bend. This can weaken the trusses, and some trusses may even fail. Thus connector plates should be examined.

Unfortunately, insulation may cover a portion of these, so it may be necessary to pull back part of the insulation to observe all of the connector plates.

Collar ties

A collar tie is a horizontal piece of wood, often a 1×6 or similar piece of dimensional lumber, that is located in the top 1/3 area of the rafter span on a gable roof. It connects to rafters on the opposite side of the ridge board or beams.

They help prevent rafters from separating or pulling away from the ridge board or beam. They also help prevent a roofs’ downward movement or collapse from the roof cover material’s weight (i.e. shingles, tiles, etc.), heavy snow loads, and unbalanced loads from wind storms.

It’s not uncommon to find rafter ties crack, damaged, pulled loose or even missing at times. They should be repaired or replaced, and doing so is usually a very easy task.

Rafter Ties

Rafter ties on gable type roofs are usually horizontal wood pieces (often 2×4’s or 2×6’s) that help keep the exterior wall tops from spreading outwardly. Normally in the third bottom area of the rafters or sitting on the exterior wall top plate.

Check for damage to rafter ties as well as their connection to the exterior walls. Should opposite exterior walls be leaning outwardly and there are rafter ties: be extra observant of the connection points to the outside walls.

Ridge Beam or Ridge Board Sagging or Damaged

Solar Panels

Roofs may sag because a ridge beam or ridge board is cracked or damaged. This may have been caused by any number of factors.

  • If a roof has been re-roofed with heavier roofing material than the original roof was engineered for, i.e. the original roof was a light wood shingle roof, and the new replacement roof is a concrete tile roof weighing 5 or 10 times more than the original roof. Then the beam or roof may sag.
  • When an old composition shingle roof becomes worn out or starts to leak, a new composition shingle roof may be laid right over the old composition shingle roof. Now the roof is twice as heavy and will possibly sag.
  • A large snow or ice storm may have dumped a heavy load of snow on the roof, more than the roof was designed to carry.

Any of the above could cause the ridge to sag, so it’s vital to check for cracks or other damage and repair everything to ensure the longevity of your roof. We have a wide range of repair and Melbourne roof restoration services at Top Glaze.

Check for wood rot and deterioration.

Roof leaks are the most common source of moisture in attics. Stains, damp, musty odours and dampness are signs of a leaking roof. Naturally, if you see buckets or pots setting about, you know there’s probably moisture.

Older roofs and roofs with damaged tiles, shingles, etc., are prone to leaking. Common areas for leaks include roof valleys, vent penetrations and chimney flashing areas.

Moisture, rot and mould weaken framing members, and over time, rafters, trusses, rafter ties and roof sheeting may structurally fail.

Wood “Dry Rot” and “Wet Rot” weakens framing members, and of the two, dry rot is the worst; basically, dry rot is more destructive and is the most serious form of fungal decay, but wet rot is more prevalent. (Read more about dry rot – sometimes referred to as “Building Cancer”)

If you can easily stick a screwdriver into deteriorated wood, then repair and remediation should be addressed sooner than later.

Identifying differences between wet rot and dry wood rot 

Wet wood rot:

  • The wood may feel soft or spongy.
  • Will often have a black looking fungus growing on it.
  • It May have a damp musty odour.

Dry wood rot:

  • Often brownish
  • May have a whitish cob-webish or cotton-wool like substance growth on the surface
  • May have “Fruiting” mushroom-like body, possibly with red spots on it

Mould and mildew

Check for mould and mildew evidence. When observed, there is generally a moisture problem and there may be wood strength issue as well, leading to sagging, bowing or waviness.

Termites and carpenter ant damage

Attics that have termites or carpenter ants may experience significant damage to wood rafters and trusses, as well as other framing members. If not treated, the lumber becomes weaker and may sag or fail, even collapsing in extreme cases.

Termites damage wood by eating the cellulose, and carpenter ants damage wood by boring holes in it (called tunnels) for their nest or galleries. It usually takes years for Carpentry ants to cause significant damage and you may see dust under the area of their tunnels. Often these ants appear in areas where there is moisture rather than dry areas.

Termite warning signs include damaged wood, frass (termite droppings) laying under the area where damage and possible small termite wings will be laying in the same area.


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