Cross Laminated Timber (CLT) Panel Deck

As part of our continuous monitoring of the latest industry guidance, we will now be including within our specifications the use of a random nailed layer of AP1 for Bauder Hot Melt (New Build) and TA 600 for Bituminous Membranes (New Build & Refurbishment), prior to the installation of the waterproofing system on a CLT deck.

This measure is intended to eliminate the risk of issues caused by excessive moisture content within the roof deck.

Why?

Following feedback from our Site Technicians and Approved Contractors, it has become apparent that the adhesion of Hot Melt and Bituminous waterproofing membranes can be adversely affected by moisture rising from Cross Laminated Timber (CLT) decks and causing de-bonding of the waterproofing system.

BS 5250 is currently reviewing its guidance regarding moisture content within timber structures.

NHBC does not currently permit the use of CLT due to significant historical claims. Following Bauder's recommendations will help reduce the risk of trapped moisture issues associated with those claims.

The original Contractor Update also referenced NHBC guidance relating to timber decks and highlighted that both CLT decks and SIP panels are excluded from the approved listing for the reasons outlined above.

Existing Specifications

Existing specifications would typically have required CLT decks to incorporate Bauder R333 Taping Strips (for Bituminous Membrane Systems) or Bauder Sprint DUO (for Hot Melt Systems) at all deck joints.

Taping of Board/Panel Joints for Bituminous Membranes

Tape centrally over joints using 200mm wide strips of Bauder R333 Taping Strip. The strips may be temporarily retained in place using clout nails prior to installation of the self-adhesive air and vapour control layer or underlayer.

Taping of Board/Panel Joints for Hot Melt Systems

Tape centrally over joints using 200mm wide strips of Bauder Sprint DUO. These should be retained by removing the release film and adhering the membrane directly to the deck.

For specifications issued prior to this update, contractors should contact the relevant Area Technical Manager to discuss project-specific requirements.

Refurbishment Specifications

Where a refurbishment specification requires removal of the existing waterproofing down to a CLT deck, a full investigation of the deck condition and moisture content must be undertaken before the installation of a replacement waterproofing system.

If moisture content exceeds 20%, or if the surface condition is unsuitable to receive the specified waterproofing system, provision should be made for replacement of the deck.

When Does This Change Take Effect?

All new specifications issued from the date of this update will include either AP1 or TA600 beneath the waterproofing system as appropriate.

Tooling for Installation of Random Nailed Layers

Bauder has received positive feedback from Approved Contractors regarding the use of nail guns to improve installation speed when fixing random nailed layers.

The installation gun referenced within the original Contractor Update was supplied by TJEP and had been used successfully on several projects.