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CONSTRUCTION KNOWLEDGE  >> THERMAL & MOISTURE >>

ROOFING & SIDING
 

1.   Why Should Roofing Be Very Important to Me?
2.   What Should I Know About Sloped (>2:12) Roofing?
3.   What Should I Know About Low Sloped (<2:12) Roofing?
4.   Why is Roof Ventilation So Important?
5.   What Should I Know About Siding?
6.   What are Waterproofing and Dampproofing?
7.   What Should I Know About Roof Specialties and Accessories?
8.   What Caulking and Sealants are Available and How do They Work?
9.   What Public Domain Documents are Available for Further Study?
10. Tricks of the Trade & Rules of Thumb for Roofing, Siding & Moisture Control:

Why Should Roofing be Very Important to Me?
 

Roof leaks seem to be one of the biggest causes of construction lawsuits. When the Owner of the project you're building moves into their new facility and gets rained on inside, he or she gets upset. So, really focus on getting the roof right on your projects. Understand the basics of the proposed roof system and then pay close attention to how things are actually getting done in the field.

Many Construction Supervisors think the roofing subcontractor has complete responsibility for the roofing and water tightness, but that's short sighted thinking. I've had Roofing Contractors go bankrupt, leaving all their workmanship issues as my problem. I've had leak problems around mechanical and electrical roof penetrations in which the responsibility isn't that clear. Finally, even if the Roofing Contractor does do the right thing and try to make repairs, it's more difficult to fix a roof than to do it right the first time and everybody's reputation gets besmirched.

So avoid the temptation to think that a first class roof will just happen, or will be someone else's responsibility. Put in the time and effort to understand the details and check to make sure those details are getting correctly installed. I know you're busy...make time for this anyway.

What Should I Know about Sloped (>2:12) Roofing?

Through most of history, roofs sloped. The roofing materials just wouldn't keep the rain and snow out of the building unless the roof had a significant (say 6:12 or 8:12 or 12:12) slope. Thatched roofs, slate roofs, tile roofs and wood shake roofs have all been used for centuries with great results. More recent history brought copper roofs, architectural metal roofs and shingles. I'm not going to explain all the different roof types here, you can find that information easily in the hyperlinks above or lots of other places. Instead, I'll cover a few critical areas.

The main areas to watch during a sloped roof installation are the ridge, the edge and valleys. The ridge (or the peak) of the roof often also works as the best location to vent the underside of the roof. Roofing venting keeps moist air that escapes from the inside of the building from condensing  on roof sheathing and causing rot, rust or mold. An effective vapor barrier at the insulation location also helps prevent rot, rust or mold. So make sure any ridge vents get special attention from the Roofing Contractors. Discuss the details, agree on how the ridge vent will be installed to prevent leaks from blowing rains and from snow/ice build-up.

The detail and workmanship at the bottom edge of the roof sometimes causes leaks. Too many times, the roof water doesn't drop off the roof edge and into the gutter (or directly to the ground). Instead, the roof water runs back around the bottom drip edge and then into the building to start the rot, rust or mold process. Make sure this detail gets discussed and properly installed.

Finally, valleys need to be installed properly. Of the many effective ways to install valleys, the main problem I've encountered is sloppiness. The agreed upon detail simply doesn't get installed in a workmanlike manner. So vigilance pays off here as well.

What Should I Know about Low Sloped (<2:12) Roofing?
 

Low sloped roofs came from modern architecture. Huge factories and warehouses became possible with low sloped roofs. In most cases, the lowest acceptable roof slope is 1/4" per 12" (or 2% slope). When I started in construction, 1% roof slopes, or even completely flat roofs, were sometimes used, but those roofs just didn't perform that well over time. Built-up roofing (multiple plies of felt adhered with hot asphalt or other adhesive) has the most history and still get used frequently. EPDM rubber roofs have become tremendously popular in recent decades. More recent popularity has come for the PVC and TPO white single ply roofs, that provide energy savings due to the lower air conditioning load of a black roof. Standing seam metal roofs also get installed on millions of square feet of pre-engineered metal buildings each year.

The Construction Supervisor should pay close attention to how the water gets off the low slope roof. It may be gutters and downspouts, roof scuppers or interior roof drains, but all of them leak if not properly detailed and installed. So discuss that portion of the work with the Design Professional and with the installer. Understand what should get done and what actually gets done.

You should also understand emergency roof drainage requirements. If the roof uses interior roof drains and one of those drains clogs, what happens? In the past, some roofs have collapsed in this scenario. The water builds up, the roof drain doesn't drain, the roof structure deflects down and allows more water to build up, the extra weight of the additional water on the roof further deflects the roof structure, and this continues till the roof collapses or leaks a boatload of water into the inside of the building. So nobody wants that, right?

The solution the Code writers put forth is emergency roof drains. If an interior roof drain clogs, there must be an emergency roof drain that will take roof water away and avoid the roof collapse. The emergency roof drains can be done in a variety of ways, but the common factor must be that roof water can only build up a few inches (less than the allowable roof load) before it drains off the roof. So when you use interior roof drains, always look for the secondary (or emergency) roof drain system and know how it works.

Why is Roof Ventilation So Important?

Rot, rust and mold. Rot, rust and mold. Rot, rust and mold. Rot, rust and mold. Rot, rust and mold. Rot, rust and mold. Rot, rust and mold. Rot, rust and mold. Rot, rust and mold. Rot, rust and mold. Rot, rust and mold. Rot, rust and mold. Rot, rust and mold. Rot, rust and mold. Rot, rust and mold. Rot, rust and mold. Rot, rust and mold. Rot, rust and mold. Rot, rust and mold. Rot, rust and mold. Rot, rust and mold. Rot, rust and mold. Rot, rust and mold. Rot, rust and mold. Rot, rust and mold. Rot, rust and mold. Rot, rust and mold. Rot, rust and mold. Rot, rust and mold. Rot, rust and mold. Rot, rust and mold. Rot, rust and mold. Rot, rust and mold. Rot, rust and mold. Rot, rust and mold. Rot, rust and mold.

What Should I Know about Siding?

Cedar wood siding, cement board siding, vinyl siding, aluminum siding, and steel pre-engineered siding all have a place in the building construction market. When the siding work begins on site, pay attention. Several siding items just need to be started right and continued to finish for a good siding job. The connection of the siding to the substrate should be understood by the actual installer. As you may know, vinyl siding nailed to a plywood substrate needs to be nailed in such a way that the nail allows the vinyl siding to move in the nailing slot due to temperature expansion and contraction. Don't assume everyone installing vinyl siding will understand this concept without any review.

Also, the spacing on the siding panels can dramatically affect the look of the project. As the first few panels are put in place, evaluate how the installers are measuring and fastening. The level of quality won't get better as they go, unless you set the standard of acceptability. Remember, as with everything else in construction, perfection is not a standard we strive for. Clearly set what tolerances will be acceptable. It may be 1/16th of an inch, but make it clear to the installers and the final project will benefit.

What are Waterproofing and Dampproofing?

Water next to basement walls tends to find its way through the wall and into the building. Remember concrete and masonry walls are rarely detailed and built to prevent the passage water. Therefore, below grade walls that could have water on the outside should have waterproofing, to prevent water on the inside.

Most waterproofing systems use a membrane placed on the outside of the wall. Types of membrane waterproofing systems include bitumen,  EPDM, Polymeric and liquid applied membranes. Each of these waterproofing systems are proprietary and you need to read through their recommendations to assure proper installation.

Dampproofing differs from waterproofing. Dampproofing protects against the "rising damp," which is the first few feet of a masonry wall above grade sucking the moisture up from the exterior soils. The capillary action that can suck the water up into the wall can cause mold, rot and stains from the salts. A dampproofing just above ground level can prevent these problems from the rising damp.

What Should I Know about Roof Specialties and Accessories?

The more penetrations through the roof, the more likely the roof leaks. Even though that statement seems, and probably is, true, most buildings have a slew of roof penetrations. Roof access hatches are often code required. Roof curbs support the roof top HVAC equipment that Owners love putting up there in the "free real estate" zone. Various pipes, vents and chimneys need to penetrate through the roof. Skylights are popular. On sloped roofs, snow guards help keep the ice and snow from all sliding down and one time and tearing off the gutters and downspouts.

The main lesson I've learned about roof specialties involves roof curbs. Since I generally didn't pay much attention to roof curbs, I was surprised years ago when we just couldn't get some roof leaks stopped in a standing seam low slope roof with some large rooftop HVAC units. What I learned was that all roof curbs are not equal, especially when used on standing seam roofs. The roof curbs we used didn't have enough taper on the higher roof edge to assure that the roof water ran around the curb, rather than built up in that location. The problem was worse with some slush on the roof or in driving winds. Standing seam roofs don't do well with any standing water on the roof. So if you need to put roof curbs on a standing seam low slope roof, make sure the curb has enough taper to shed the upstream water.

What Caulking and Sealants are Available and How do They Work?

There are lots of types of caulking and sealants, but I don't think you really need to learn the different products and what they do. I think the most important thing you should know about caulking is that it works in 2D but fails in 3D. I'll explain. As I covered in the General Technical Knowledge, Basic Structural section, expansion and contraction causes significant movement in larger buildings.

Think about a brick wall with a control joint. As the brick expand in warmer weather, the joint gets smaller. Conversely, cold weather makes the brick contract and a wider joint. The occupants of the building don't want the rain blowing in through this movement joint, so we caulk it. The figure below illustrates how the caulk stretches in the 2D sketch, when the caulk only attaches to the brick on either side of the joint. On the other hand, if the caulk also bonds at the bottom of the joint (say to some mortar), then it moves in 3D and often fails, tearing away from the brick and not keeping the wall weather-tight.

What Public Domain Documents are Available for Further Study?

The US Department of Defense provides a detailed general resource for roofing applications.  This 69 page handbook is officially called Roofing, UFC 3-110-03 (September 2006).

Another resource, more useful in the design of roofs, is the US Dept of Defense Commentary on Roofing Systems. It has 225 pages of information , and is officially named UFC 3-330-02A (March 2005).

Specific to Metal Roofing, this 21 page document produced by the US US Army Corps of Engineers, titled TI 809-29 (August 1998), provides details regarding the structural considerations needed in designing a metal roof.

The US Department of Defense provides a detailed general resource for Joint Sealing for Buildings.  This 29 page manual is officially called UFC 3-190-01FA (November 2003).

Tricks of the Trade & Rules of Thumb for Roofing, Siding & Moisture Control:

1. The roof is your problem, no matter how it's subcontracted, so pay attention.
2. Think if the roof and roof venting will actually work to prevent rot, rust and mold.
3. The low slope roof must have emergency drainage if the roof drain clogs.
4. Approve the siding quality level in the first day of their work.
5. Caulking works in 2D and fails in 3D.