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Skip Sheathing Guide: Is it Worth it?

Skip Sheathing Guide: Is it Worth it?

Skip Sheathing Guide: Is it Worth it?

Skip sheathing refers to the roof sheathing with gaps. 1x4 boards of plywood or oriented strand board (OSB) are nailed onto the rafters with spacing between the boards. This spacing is useful in allowing air to flow through the roof and drying out the moisture.

This article provides a detailed guide on skip sheathing and how it's installed.

What is Skip Sheathing?

Skip sheathing is a form of roof sheathing in which the wood boards are placed with a certain spacing between them.

Normally 1x4 or 1x6 wooden boards are used in skip sheathing, with a maximum spacing of 3.5” in between.

Then, nail the sheathing directly onto the roof rafters to make a firm connection.

Next, attach shakes and shingles to the sheathing.

The boards installed this way have openings between them, allowing air to flow under the wooden shakes and shingles.

This airflow moves laterally, allowing for faster drying of these members from underneath.

Skip Sheathing.
Skip Sheathing

Is Spaced Sheathing the Same as Skip Sheathing?

Spaced sheathing is an alternate term used for skip sheathing.

Both these terms refer to the same process of installing sheathing with gaps in between the wooden boards or shakes over the rafters in roofs.

Another term used for skip sheathing is gapped sheathing.

Why is Skip Sheathing Important?

Wooden roofs absorb water and rot.

In addition, they are exposed to intense heat from the Sun, causing bending in the wooden shakes due to uneven drying.

This bending or curving is undesirable as it leads to cracking and, ultimately, splitting of the shakes from the roofs.

After the wooden shakes crack and split, the sheathing is likely to absorb even more moisture which causes the underlying wooden boards to degrade.

If the damage is left unchecked, continuous freezing and thawing of water comes into effect and causes further degradation of the wooden members.

Allowing air to flow through the roof can significantly reduce these issues.

Skip sheathing allows the passage of air that facilitates faster drying of the roof members, enhancing the durability of the roof.

Advantages of Skip Sheathing

Skip sheathing aids in reducing moisture damage on wooden roof structures by enabling airflow.

The spacing provided by skip sheathing also reduces the cost of materials since it requires less material to create the layer.

Additionally, the shakes and shingles remain attached to skip sheathing for long periods of time and do not have to be replaced often.

Wooden Roof Configuration.
Wooden Roof Configuration.

Limitations of Skip Sheathing

Skip sheathing is very effective when provided on wooden roofs supporting wooden shakes and shingles.

However, the spacing cannot be supported by asphalt composite shingles as it does not form a solid deck.

Skip sheathing is also not effective in regions with heavy snowfall and windy rains.

Furthermore, re-sheeting over degraded skip sheathing using small pieces of lumber is not enough.

Nailing small new pieces between old skip sheathing leads to cracking.

Thus, full-length solid sheets must be applied on top of the old skip sheathing, which can be very expensive.

Resheeting over Skip Sheathing.
Re-sheeting over Skip Sheathing.
Advantages of Skip SheathingLimitations of Skip Sheathing
Reduce moisture damageUnsuitable for asphalt composite shingles
Cuts material costsIneffective in areas with heavy snowfall and windy rains
Prolongs the lifespan of shakes and shinglesFull-length solid sheets are required for re-sheathing
Advantages and Limitations of Skip Sheathing

Spacing in Skip Sheathing

For wooden shakes and shingles, 1x4 boards are used in skip sheathing with 10” and 5” spacing, respectively.

In the case of concrete tiles, 1x4 boards are not enough to carry the weight, so 1x6, 1x8, or 2x4 boards are used with 12” to 14” spacing.

Metal plates are lighter, and usually, 1x6 boards with 24” spacing provide sufficient strength to support them.

How to Install New Sheathing Over Old Sheathing?

Installing a new sheet over skip sheathing is quite common.

It is done when a solid surface is required over the roof or as a design choice when shingles and shakes have to be installed.

To do this, first, select the material for your new sheet. Generally, plywood or OSB sheets are applied over old sheathing.

Check with your city's building department and building codes to see the required size of sheet panels.

Afterward, cut the plywood or OSB panels accordingly and start installing them from any corner of the roof.

The size of the panels should be such that they fit center to center between two rafters. This helps in nailing them properly.

You will notice that at some intervals, there is no surface available for nailing.

In such instances, install filler wood between the skip sheathing to act as a nailing surface.

Keep repeating the process until the whole roof has been applied with a new sheet of wood.

Installing Plywood sheet over Skip Sheathing.
Installing Plywood sheet over Skip Sheathing.

Types of Skip Sheathing

There are a number of materials that can be used in roof skip sheathings, such as OSB, plywood, and wood boards.

Each material used in sheathing must be specially certified and exterior graded to ensure its long life.

The certification indicates that the material has been treated with chemicals and is water resistant.

This is important because sheathing is constantly exposed to harsh exterior weather conditions like precipitation and snow.

Steel and concrete are also used in roof sheathing; however, they are not preferred for skip sheathing.

Types of Skip SheathingDescription
Wood Board SheathingUtilize wooden planks for sheathing, but can rot over time
OSB SheathingCost-effective and durable
Plywood SheathingMore-water resistance and durable
Types of Skip Sheathing

Wood Board Sheathing

The original material used in the roof sheathing back in the 20th century was the local wood.

Planks of wood were cut and installed to form a base over the roofs of houses. Later on, shingles and shakes were installed on top of the base.

Spaces were left between the panels to allow airflow for faster drying of the wood.

Due to progressive rotting, the shingles and shakes would fall off, and they would have to be replaced with new ones.

It was due to this problem that stronger roof sheathing materials such as plywood and OSB were later introduced.

Oriented Strand Board (OSB) Sheathing

OSB is a synthetically manufactured material made from different wood components.

Special adhesives are used to make bonds between the layers of an OSB board.

OSB is a relatively new engineered material that provides strength and uniformity at a cheaper rate than its alternatives and has gained popularity over the last few decades.

OSB board
OSB board

Plywood Sheathing

Plywood is another common sheathing material that is made of numerous wooden layers held together by special adhesives.

This layering helps in making plywood a thick surface for nailing purposes and helps avoid the warping and shrinking of the boards.

Plywood is also similar to OSB in providing strength and durability; however, it has an additional benefit in terms of moisture resistance.

Plywood board.
Plywood board.

Skip Sheathing vs Modern Roof Sheathing

In regions with heavy snow, rain, and strong winds, it's common to use uniform roof sheathing made from synthetic materials and roof underlayment.

Air can pass through these materials without the need to provide spacing between their panels.

This modern approach of roof sheathing enables more airflow making it more efficient as compared to wooden skip sheathing.

Conclusion

Skip sheathing is a process applied to roofs to enable airflow that leads to faster drying of wooden members.

It is done by fixing boards made of OSB or plywood over rafters, having spaces in between.

This spacing allows for air to flow through and dry out the moisture in the roof components in an even manner.

It is an efficient way of ensuring the longevity of wooden panels, shakes, and shingles.

Note that skip sheathing is only effective in wooden roofing. It cannot be incorporated into concrete and steel roofs.

Furthermore, in regions with heavy snowfall and windy rains, skip sheathing is not very effective in drying out moisture.

The roof sheathing in such regions is generally made of modern synthetic materials, through which air can easily pass, and no spacing is required.

Frequently Asked Questions (FAQ)

Are Roof Decking and Skip Sheathing the same?

No roof decking and skip sheathing are not the same things.

Roof decking refers to the application of continuous wood panels to make a uniform deck over the rafters of a roof.

Whereas in skip sheathing, the wooden panels are not installed continuously; rather, they have spaces in between them.

What Type of Sheathing Is Best for a Roof?

Oriented strand board (OSB) is the most durable material being used in sheathing roofs.

It is also used in making sheets which are used in the re-sheeting skip sheathing.

What is the Thickness of Plywood and OSB Sheathing?

The sheets made from plywood should be at least 1/2” thick.

On the other hand, OSB sheets should have a minimum thickness of 7/16”.

About V Susan

Hi! I'm Susan. I am passionate about woodworking, general DIY and home improvement. If you'd like to connect with me or talk about something you like at mellowpine, drop me a mail at susan@mellowpine.com

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V Susan

Hi! I'm Susan. I am passionate about woodworking, general DIY and home improvement. If you'd like to connect with me or talk about something you like at mellowpine, drop me a mail at susan@mellowpine.com

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