Guidance on the Use of Oak in Construction

In this article we look at the use of Oak in construction, considering the following three types:

 

  • Green Oak - Recently felled oak with a moisture content between 60%-80%
  • Air Dried Oak - Naturally stored oak with a natural seasoning process moisture content up to 30%
  • Kiln Dried Oak - Processed seasoned timber with a moisture content between 15% and 20%

 

Identifying Green, Air Dried or Kiln Dried Oak

 

Where timber has been dried and has a moisture content less than 10%, it will usually be marked with a stamp saying “DRY” or “KD” (for kiln dried), however, if timber has been cut or machined, it is likely these stamps are not visible. In such circumstances it is recommended that proof of purchase confirming that timber is kiln dried should be provided.

 

This article reviews various scenarios where oak could be used and beneath each, there is a table detailing whether it is acceptable to meet Premier Guarantee warranty standards.

 

The table relates to the oak type and the applicable policy as a simple ‘yes’ or ‘no’, to determine whether it can be accepted. Please note that there may be additional guidance required which will have been clarified for each scenario.

 

This article covers most examples where oak may be used in construction; please contact your surveyor for further clarification if required.

Environment 1 - Through wall Oak Framed Construction forming part of the waterproof envelope
 

New Homes

Social

Self-build

Completed

Commercial

Green

No

No

No

No

No

Air Dried

No

No

No

No

No

Kiln Dried

No

No

No

No

No

Environment 2 - Internal frames not forming part of the waterproof envelope including purlins and trusses floor joists
 

New Homes

Social

Self-build

Completed

Commercial

Green

No

No

No

No

No

Air Dried

No

No

No

No

No

Kiln Dried

Yes

Yes

Yes

Yes

Yes

 

 

 

 

Environment 3 - Open canopies
 

New Homes

Social

Self-build

Completed

Commercial

Green

No

No

No

No

No

Air Dried

Yes*

Yes*

Yes*

Yes*

Yes*

Kiln Dried

Yes

Yes

Yes

Yes

Yes

 

*The canopy should be structurally independent from the dwelling and cover an area not exceeding 3m square.

Environment 3 - Enclosed porches
 

New Homes

Social

Self-build

Completed

Commercial

Green

No

No

No

No

No

Air Dried

No

No

No

No

No

Kiln Dried

Yes

Yes

Yes

Yes

Yes

 

Environment 4 - Oak embedded into the ground
 

New Homes

Social

Self-build

Completed

Commercial

Green

No

No

No

No

No

Air Dried

No

No

No

No

No

Kiln Dried

No

No

No

No

No

 

Environment 5 - Windows and doors
 

New Homes

Social

Self-build

Completed

Commercial

Green

No

No

No

No

No

Air Dried

No

No

No

No

No

Kiln Dried

Yes*

Yes*

Yes*

Yes*

Yes*

 

*Please apply guidance in Chapter 7.4 of the Premier Guarantee Technical Manual with regards to timber windows. 

Environment 6 - Second fix joinery e.g. floor boarding, skirting boards, internal doors, stairs
 

New Homes

Social

Self-build

Completed

Commercial

Green

No

No

No

No

No

Air Dried

No

No

No

No

No

Kiln Dried

Yes

Yes

Yes

Yes

Yes

 

Note: reclaimed oak will be accepted where it is proven to have a moisture content below 20%.

Environment 7 - Attached outbuilding structures - including garages
 

New Homes

Social

Self-build

Completed

Commercial

Green

No

No

No

No

No

Air Dried

No

No

No

No

No

Kiln Dried

No

No

No

No

No

Environment 8 - Detached outbuilding - including garages
 

New Homes

Social

Self-build

Completed

Commercial

Green

QGU*

QGU*

Yes**

Yes**

Yes**

Air Dried

QGU*

QGU*

Yes**

Yes**

Yes**

Kiln Dried

QGU*

QGU*

Yes**

Yes**

Yes**

 

*Quote Generation Unit (QGU) Referral - these buildings should not be included in the New Homes or Social Housing policies. Please contact our QGU department to arrange for exclusion of any timber building from the policy.

 

**Detached outbuildings are not included in these policies. 

Environment 9 - External cladding
 

New Homes

Social

Self-build

Completed

Commercial

Green

Yes*

Yes*

Yes*

Yes*

Yes*

Air Dried

Yes*

Yes*

Yes*

Yes*

Yes*

Kiln Dried

Yes*

Yes*

Yes*

Yes*

Yes*

 

*Take into consideration movement and potential shrinkage; ensure that fixings are compatible with oak. Substrates and drained/ventilated cavities must comply with the relevant section in Chapter 7 of the Premier Guarantee Technical Manual

Environment 10 - Mock Tudor Cladding
 

New Homes

Social

Self-build

Completed

Commercial

Green

No

No

No

No

No

Air Dried

Yes*

Yes*

Yes*

Yes*

Yes*

Kiln Dried

Yes*

Yes*

Yes*

Yes*

Yes*

 

*Fix cladding onto a continuous render substrate (not render infill between timbers). Timber should be fixed using stainless steel screws that are at least 3 times the depth of timber and appropriate for the substrate. Substrates should comply with the relevant section in Chapter 7 of the Premier Guarantee Technical Manual