Ask NADRA: Deck Ventilation Requirements

April 30, 2011 | Ken from Orangeburg, SC asks:

“I am wondering is there a minimum height requirement for a
deck to allow for adequate ventilation under the deck. Is this
measured to the top or bottom of the decking timber?”

Glenn Mathewson, NADRA’s Technical Advisor, responds:

Hello Mr. Panitt.

Thank you for turning to NADRA with your questions about the Decking and Railing Industry. We are certainly happy to provide you guidance. The International Residential Code (IRC) and International Building Code (IBC) do not specifically regulate the ventilation of areas underneath exterior decks. IRC Section R408.1 describes the ventilation requirements for under floor spaces, including the minimum net free area, but it is in reference to areas under buildings that are enclosed by foundation walls. While it would certainly be good practice to maintain moisture control under decks that are very low to the ground, its not part of the minimum standard set forth by the IRC. However, in the case of manufactured decking or other products, the installation requirements of the manufacturer are essentially part of the code. This may be from a direct reference to, such as section R317.4.1 in the 09 IRC for wood/plastic composites or through approval as an “alternative”.
I know at least two prominent tongue-and-groove composite decking products that require a minimum height above grade to make up for the lack of air flow between the boards. In both cases the distance was 12 inches of vertical space beneath the bottom of the framing, though the percentage of perimeter where it was required varied. You must always adhere to manufacturer’s installation instructions, not only for good practice, but also for code compliance.
For spaced deck boards, the gaps would likely suffice for ventilation. They may be narrow, but they’re evenly dispersed. One thing to consider, however, is the size of the gaps and the material used. If swelling of wood, expansion of thermoplastics, proximity to heavy autumn leaf fall, long snow coverage or poor maintenance/cleaning is likely, the gaps may close. In that case, additional ventilation openings or greater clearance to grade would be a good plan.

I hope this information is of assistance to you and the visitors of the NADRA blog.

Sincerely,

Glenn Mathewson, MCP

Ask NADRA: Is Fungus Destroying CCA Wood?

April 30, 2011 | Wallace from Midway, GA asks:

“[What do I] need to know about fungus destroying CCA lumber?”\

Huck DeVenzio of Arch Wood Protection Reponds:

From your question and e-mail address, I’d guess that you have heard reports from a guy (Sam Brooks) saying that there is a strange fungus destroying CCA-treated wood in coastal areas. He says his company has a solution.

I’m amazed that this non-story is getting as much attention as it has. From all we have been able to piece together, there is no strange and destructive fungus. The photos he shows involve an occasional condition called tracheid separation or salt-killed wood. It does not involve a fungus and it is not a failure of CCA preservative. It is caused by wicking of salt into some pieces of wood. A document (link provided below) published by experts at Mississippi State University is attached; it explains the phenomenon. This was written in March, largely to counteract the assertions appearing in the Charleston-Savannah area. I have another technical paper if you need more information.

This “salt kill” can cause problems for marine piling, but it tends to be scattered and it is not caused by fungi. I do not know anything about the solution offered by Mr. Brooks, but you have to be suspicious when he doesn’t even understand the cause of the problem.

Click here to read the report from Mississippi State University.

Ask NADRA: Preserved Wood For Wet Climate

April 26, 2011 | A concerned homeowner in British Columbia asks:

I have a 3-foot crawlspace which has a damp concrete floor whenever we get heavy rain. Consequently, the exterior pony walls carrying the fiberglass insulation are beginning to decay. Can I replace the pony walls with preserved wood and not put a finish cladding on it? Is there a toxicity factor here if the wall is not properly sealed? Timing and budget are not big factors here as much as having the job done right. Thank you.

Huck DeVenzio of Arch Wood Protection Reponds:

If you purchase properly treated wood (we, of course, recommend the Wolmanized brand) intended for ground contact, you can be confident that the wood will resist fungal decay for many decades, and you don’t have to be concerned with sealing or cladding. Treated wood has been used for years in Permanent Wood Foundations (made of treated studs and treated plywood), framing for all homes in Hawaii (where termites necessitate this), and for the sill plate of nearly all homes in North America. In all of those applications, many left unfinished, there is not a single known adverse health or environmental incident from the preservative in the wood.

Because of the dampness and your past problem, I would try to get wood treated for ground contact, even if most of the lumber will be above ground. That gives you an extra measure of security.

You can probably find properly treated wood at a lumber dealer near you. I hope this helps.

Ask NADRA: Deck Stair Lighting Codes

March 21, 2011 | Lainie Sleppin of Mid-State Lumber asks:

“I am getting a number of calls regarding the code on deck stair
lighting, no pun but can you shed any light on this code so I can
advise correctly. We are talking about guys in the NJ market.

Thanks for your help and have a great weekend.”

Glenn Mathewson, NADRA’s Technical Advisor, responds:

Hello Lainie,

Thanks for your confidence in NADRA, the voice of the decking industry, to be your “go to” when you need quality information on the decking and railing industry. I understand your contractor customers in the New York and New Jersey area have been asking questions lately about lighting at deck stairways. I am happy to provide you assistance in better understanding the requirements of the 2009 IRC in this regard. Many people I discuss this with are surprised that when you read Section R303.6 there are two requirements…one for the location of a lighting fixture, and one for the illumination of the stairway. They are not one in the same.

I have copied below the discussion from ICC’s deck code book, Deck Construction based on the 2009 IRC. Continue reading “Ask NADRA: Deck Stair Lighting Codes”