Sheathing boards can be used throughout the construction of homes both in new build properties and when renovating existing elements and can contribute to improving energy efficiency.
In this blog, we explore the properties that different types of sheathing boards bring to a building, the range of sheathing materials available, and how certain options, such as wood fibre boards, can also provide the added benefit of an insulating layer within the home to help improve energy efficiency.
What are sheathing boards and what materials can they be made from?
Sheathing boards are rigid boards that are used to cover construction elements within wall and roof assemblies in the external fabric of a building. They provide a solid, flat surface to which other materials essential to the overall performance of the construction can be applied, such as insulation, membranes, plasterboard, or roofing finishes.
There are two types of sheathing board:
Structural sheathing boards
The main purpose of this type of sheathing board is to provide structural stability to the building fabric. They are typically made from diffusion-closed materials such as gypsum, cement, OSB (Oriented Strand Board) and plywood.
Insulating sheathing boards
These sheathing boards help to improve the thermal performance of a structure and are diffusion open, so they allow moisture vapour to pass through. These insulating diffusion open sheathing boards are typically made from wood fibre panels.
The selection of the most suitable sheathing boards and their location within the external fabric will depend on the structural and specific functional requirements of the project such as moisture control strategy and insulation requirements.
What are the key functions of structural sheathing boards in a home?
Structural sheathing boards are designed to provide additional structural capacity to wall and roof elements. When fixed to the frame of a construction element within the home, they help to stiffen the structure and improve its resistance to movement. They can also assist in distributing loads across the frame, reducing the strain on individual structural members.
Structural sheathing boards form a continuous layer over a construction element, offering protection against external factors such as wind and rain and, in some cases, fire, as well as providing resistance to physical impact.
How can insulating sheathing boards contribute to improved energy efficiency?
Insulating sheathing boards can help to improve the energy efficiency of homes by reducing the effects of wind washing and by adding an additional layer of insulation to the building fabric.
Insulating sheathing boards can be:
- Fixed to the inner or outer surface of external walls
- Installed above or below the rafters in pitched roofs
- Installed above or below the joists in flat roofs
Insulating sheathing boards can reduce the effects of wind washing
When correctly installed with tight joints and no gaps, insulating sheathing boards form a continuous barrier that reduces the opportunity for uncontrolled draughts to enter the building. This helps to limit the impact of 'wind-washing' and reduce heat loss through gaps in the building fabric. By limiting heat loss, the demand on the heating system is reduced, which in turn improves the overall energy efficiency of the home.
Insulating sheathing boards can help to increase thermal performance
Adding an additional layer of material to a construction in the form of sheathing boards helps to increase its resistance to heat transfer and can improve its thermal performance. The extent of this improvement depends on the thermal conductivity and thickness of the sheathing board used. The lower the thermal conductivity of the board, the better it will be at slowing down the passage of heat through the board.
Sheathing board material | Typical thermal conductivity (W/mK) | Typical density (Kg/m3) |
Wood fibre board | 0.048 | 250 |
OSB | 0.13 | 650 |
Gypsum | 0.19 | 870 |
Cement | 0.26 | 1360 |
Wood fibre boards have one of the lowest thermal conductivities of sheathing boards and can therefore help to improve the insulting performance of a home and its energy efficiency
What is the advantage of using both structural and insulating sheathing boards in the same application?
Where structural diffusion-closed sheathing boards are installed on the outside of a framed system they provide the support required, however there is a risk that moisture may be trapped behind them and condense on the frame without any means of escape. If they are instead installed on the inside of the frame and insulating wood fibre diffusion open sheathing boards are fixed externally, any moisture finding its way to the frame can safely diffuse through the wood fibre boards.
This combination of sheathing boards forms a robust approach that helps to provide the structural integrity required by the building fabric whilst incorporating a diffusion open insulating sheathing layer to enhance the ability of the building to manage moisture risk.
Where can I find out more information about wood fibre sheathing boards?
STEICO has a range of insulating wood fibre sheathing boards. They are all diffusion open with a tongue and grooved (T&G) profile to provide a continuous protective sheathing layer that can allow the fabric of the building to breathe.
With a compressive strength of 200 Kpa and a lambda value of 0.043 W/(m*K) STEICOuniversal dry is a sheathing board that can significantly support the thermal performance of the construction assembly.
STEICOsafe is a T&G sheathing board that has a directly bonded membrane for increased weather protection for roofs or when used behind brickwork facades.
To enquire about using our sheathing boards on your next project, please contact us and our expert team will be happy to help.