I’ve had this Q & A page at JLC online on my to do list for a while now to post up here for you all…while the discussion is about drainage problems on low slope roofs, the photo they use is a deck over living space with tile on it and ponding water. And of course, decks over living space with tile or pedestrian traffic coatings on them are roofs as well, just that we walk on them too.
Frank discusses how a roof deck can pond water even when it’s “built to code” from loads placed on the deck. Recommended reading for designers, architects, builders, waterproofers and anyone interested in increasing their knowledge and skills.
Q. Can deflection of a low-slope roof cause ponding? How can this be avoided?
A. Frank Woeste, P.E., professor emeritus at Virginia Tech, responds: Historically, structural designers and builders have assumed that a design slope of 1/4 inch per foot (1:48) is sufficient to prevent ponding action, thinking that the installed roofing system will maintain at least a 1:48 slope in-service as required by some roof covering systems. However, in many cases and for different reasons, ponding on limited areas of low-slope roofs is common. That’s due to roof deflection, which over time can cause water to collect in some areas of a roof where the design slope for drainage is not adequate, and in fact changes from a “positive” drainage slope to a “negative” slope (see photo below).
DOWNLOAD THE PDF VERSION OF THIS ARTICLE. (666.96 KB)
Here at DeckExpert.com, I often hear someone say “the flashing leaked and the deck failed”. I always ask, how did the flashing leak? In my opinion, if the deck waterproofing system is installed in such a manner that the entire piece of flashing, the horizontal piece nailed to the deck and the vertical leg that goes up the wall is completely embedded in waterproofing, the flashing basically cannot leak. Drip edges covering the building materials below won’t leak unless the coating has lost it’s bond with the metal. I often find that happens when gutters are nailed through the drop of the drip flashing and the metal is deflected.
The misnomer in my opinion in the industry is to think of flashing as “waterproofing”. It is not primarily waterproofing. What the flashing is for is to provide a termination point for the deck waterproofing system to end to. Metal flashing is simply what we use to do that.
Now let me clear, the flashing’s still must be integrated properly into/with contiguous weather resistant barriers that are being installed by other trades-where building paper comes down and over the flashing for the deck. Sequencing is essential when it comes to installing weather barriers and typically the low slope roof and deck areas are weathered in first.
Edge/drip flashings still must be installed in a manner that they are placed over building materials below them so water runs over, away and off.
Flashing materials are commonly galvanized/bonderized metals, copper and stainless steel. When using any of these, proper preparation of the metal is essential prior to terminating the coating to it. Bright shiny galvanized I don’t recommend at all as it’s very difficult to clean and prep properly in the field for our work’s requirements. I recommend “bonderized” metal flashing instead. It’s basically clean so it usually just needs to be wiped down with a damp rag to remove dust and contaminants. Copper and stainless steel both require being sanded heavily to “etch” the metal. I use a 4″ grinder with the sanding flappers in a 50-36 grit paper to cut into the metal. I then prime the metal with a liquid based mix of the base coat so it’s loose with polymer and I brush it out onto the flashings. I then use fiberglass and resin to finish waterproofing the vertical legs of the wall to deck. See picture below for an example. Completely encasing the L flashing makes sense to me, it eliminates the possibility of water sitting at the wall and finding metal to attack. I’m also seeing this detail in Pli-Dek and Duradeck’s details, and I hope to see other manufacturer’s follow suit if they haven’t already.
Following the collapse of the balcony in Berkeley, that killed 6 and seriously injured 7 others, the California Building Safety Commission adopted me regulations on building and waterproofing Elevated Exterior Elements EEE for short.
The adoption of these emergency regulations will increase balcony safety standards by increasing load design, using decay resistant wood and Inspections of waterproofing before covering with other materials, such as a concrete overburden.
Testimony from the Irish families and victims has helped cause these changes. Jackie Donohue, mother of one child killed in the collapse has been leading the charge in bringing changes to balcony construction along with requiring inspections.
After Berkeley adopted ordinates requiring inspections, over 800 balconies in that city alone have been found to be deficient.
As winter starts heading into spring you may have looked out at your deck and heaved a sigh knowing you have a choice to make this year…replacing that old rickety wood deck or the fading, sagging composite deck that was supposed to last 30 years. What to do what to do? Go back to a wood deck using exotic Ipe and hope that lasts longer and has less maintenance? Use the newest and “greatest” composite?
While the wood and composite markets currently dominate the deck market, the end user is getting tired of the limited color choices of composite decking available at lumber stores and doesn’t want to wait for a special order with it’s various requirements and doesn’t really like the thought of the maintenance that wood decks require. The newest choice available is actually a choice that’s been around for a long time, it’s just that not many knew about this choice til now.
The new “choice” for decking is rapidly becoming solid surface walking deck systems installed over a plywood substrate on conventional doug fir or pressure treated framing. Solid surface decking systems offer many advantages over it’s wood and composite competitors. Some of those advantages are
Waterproof! These decks can waterproof and give you a walkable surface on a roof deck, dry in a patio below, keep a storage area dry underneath. Increases your homes value!
Cost competitive. Framing costs are the same as for decks receiving wood/composite decking. Plywood and the waterproof coating system often costs less than composite decking and almost always less than exotic hardwoods.
Less Maintenance! No sanding, staining and sealing every year. Most waterproof deck systems require resealing every 3-5 years. Clean them off easily using Simple Green, water and a hose and brush.
Unique Looks! Waterproof decks can look like anything you want-wood (yep), tile, stone, brick, stained, stamped…the designs are virtually unlimited!
Look at our deck finishes, you’ll see some of the many various finishes available that can set you apart from the rest of the pack.
The balcony that collapsed in June of 2015 in Berkeley, killing 6 and severely injuring 7 other Irish students has been found, after analysis by forensic scientists, to have been constructed improperly. As a result, the Contractors State License Board has filed through the Attorney General’s Office an accusation against Segue Construction, the general contractor.
The allegations are serious, not following plans without an architects approval will land you in hot water with CSLB. It has also resulted in 6 dead people and 7 injured. The weight of that alone would crush me, yet these people running Segue are conscienceless snakes that sought to blame the victims. How do they look in a mirror?
The accusation lists out specifically the contractors failures, from not using pressure treated materials, to using OSB board where their project manual said it was specifically not acceptable, to failing to cover and protect the deck until it could be waterproofed to failing to waterproof it properly.
Read the accusation by clicking here. Alternately you can read the specific allegations below. The accusation is a public document and the CSLB has posted it as a public service to help warn consumers, as they feel that Segue is a threat to the public. Segue is afforded due process and can defend against the accusation, including even if/when their license is suspended or revoked. Another case I’m familiar with has dragged on since October of 2013 and still proceeds today so justice may take a while here too.
Full disclosure-I just got one to test from Wagner, free of charge.
Wagner Meter, long a renowned manufacturer of moisture measuring tools for the woodworking, logging and flooring industries, has recently introduced a new tool geared for home inspectors and contractors. The Wagner BI2200 Moisture Meter is a handy tool for measuring relative moisture content of many building materials-stucco, plaster, drywall, tile, shingles etc.
As described by Wagner- The BI2200 inspection moisture meter is ideal for building or home inspections and is designed to provide comparative, relative moisture content readings for common building materials – stucco, plaster, drywall, tile, shingles, roofing, linoleum, wood and more. From their website-
Materials to Measure
Stucco, plaster, drywall, tile, shingles, roofing, linoleum, wood and more.
Specifically designed for the building or home inspector, the BI2200, using state-of-the-art electromagnetic wave technology, provides a non-invasive tool for measuring a wide range of materials including wood, synthetic stucco, plaster, drywall, insulation materials, ceramic tile, shingles, linoleum, concrete and more.
The BI2200 Building Inspection Moisture Meter provides a general comparison moisture indication for inspection applications that only require relative* moisture content (MC) readings. By establishing a known baseline dry MC relative reading on a building material, the BI2200 can then compare and pinpoint elevated MC problem areas or conditions.
The BI2200 is programmable for numerous building materials and its two-button control makes one-handed operation simple. Designed with a Teflon pad to protect the sensor area on rough or abrasive surfaces, the BI2200 can provide a relative* MC reading on building materials without damage to the materials surface.
The BI2200, with its Press and Hold feature, lets you get into tight places without needing a visual line to the meter display. Beneath a sink, under a cabinet overhang or in a tight corner, with the Press and Hold feature you can take the relative* MC reading and the display holds the reading once the meter is removed, letting you quickly and easily document the readings during your inspection.
Easy to use and with a wide range of programmable building materials, the BI2200 is a reliable, state-of-the-art tool for the building or home inspection industry. *The BI2200 does not give precise MC percentages but is designed to provide a comparative relative MC reading for each material inspected in order to identify problem or potential problem areas in a building or a home.
Size & Weight:
Length – 4 9/16″; Width – 2 3/4″; Height – 1 1/16″; Weight – .37 lbs Power:
9 volt battery
Auto Power Shut Down – 60 seconds Control:
Two button control for on/off and material settings Press & Hold feature Depth of Measurement:
3/4″ Moisture Content:
Relative 5% – 32% Scanning Area:
1 1/2″ x 2 1/2″ Material Setting:
Selectable setting .20 – 1.0 Calibration:
Verifiable at factory Other
1 Year Warranty
Carry Case with Belt Clip Included
Teflon® pad protects sensor plate from abrasive surfaces
I’ll be testing the unit out thoroughly over the next few months and writing up what I have found with it, limitations, other uses for it, accuracy etc. Watch for more info! Do you have one? Let me know what uses you’ve found for it.
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