BSC Information Sheet 304Integrating Deck Ledger Board with

Drainage Plane for All Climates

This Information Sheet has been prepared by Building Science Corporation for the Department of Energy’sBuilding America Program, a private/public partnership that develops energy solutions for new and existinghomes. The views and opinions of authors expressed herein do not necessarily state or reflect those of theUnited States government or any agency thereof.

For more information about Building America go to www.buildingamerica.gov

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Flashing Over Deck Ledger

Ledger flashing directs water out over deck ledger

Membrane flashing integrates metal flashing into the wall drainage plane

Sheathing tape seals membrane flashing to drainage plane/sheathing

Deck joist ends treated to reduce absorption of water

Integrating Deck Ledger Board withDrainage Plane

Maintaining drainage plane continuity at deckledger locations provides a particular challenge.It is common practice to install a completeWRB on a wall assembly before attaching a deckledger. Then, when the deck ledger is attached,structural connections at this location breechthis water control layer or WRB. Pressedagainst the water control layer, the ledger acts ashorizontal dam interrupting drainage andpotentially directing water to fastenerpenetrations and into the wall. Even where thewall system protection remains in tact, theledger board itself would be vulnerable tomoisture degradation if not protected. Otherbuilding elements, such as mounting blocksused for the attachment of lighting fixtures, maypresent similar conditions as those describedabove. The techniques presented in thisInformation Sheet may be applied to deckledgers as well as related elements.

Careful detailing and flashing of this connectionis necessary for both the integrity of thebuilding’s drainage system and for the durabilityof the deck structure.

The diagram to the right shows flashing over adeck ledger board. The top of the flashing isintegrated into the wall drainage plane (In thiscase, insulating sheathing installed in acontinuous manner with seams taped alsofunctions as the drainage plane). The ends ofthe joist should be treated with a sealant toreduce the absorption of water at the end of thejoist.

Where the drainage plane is applied over thesheathing material as a separate component – aswould be the case for housewrap or buildingpaper applied over structural sheathing – a waterproof membrane should be installed betweenthe ledger board and the sheathing. Thediagram on the following page illustrates theapplication of ledger board flashing in thissituation.

BSC Information Sheet 304for All Climates

Deck ledger board © buildingscience.com 2 of 2

WRB Behind Deck Ledger

Drainage plane above ledger to lap over flashing which is placedover waterproof membrane

Drainage plane to be tucked under waterproof membrane belowledger

Deck joist ends should be treated to reduce absorption of water

Saddle Flashing

Deck ledger flashing to lap over saddle flashing.

Saddle flashing may also be used for railingconnections

Suggestions for Further Research:

“Rain Control in Buildings,” Building Science Digest-013, www.buildingscience.com.

“Understanding Drainage Planes,” Building Science Digest-105, www.buildingscience.com.

“Increasing the Durability of Buildings,” Building Science Digest-144, www.buildingscience.com.

Lstiburek, Joseph W.; Builder’s Guide Series, Building Science Press, 2006.

Lstiburek, Joseph W.; Water Management Guide,. Building Science Press, 2006.

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