Q & A Building Codes
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Q & A Building Codes
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I specialize in roofing and waterproofing. I inspected over 450 residential roofs in 1996 alone, in Western Pennsylvania. I would say, not more than 10 roofs that I inspected in 1996 met the code, the manufacturer's specifications and/or the industry standards.
The code books that I refer to are; CABO One and Two family Dwelling Code and The BOCA National Building Code, depending on the municipality that the residence is located in. I also refer to The National Roofing Contractors Association (NRCA) Roofing and Waterproofing Manual. Here are a few of the roofing problems I see every day:
- 1. Fasteners are located too high. Fasteners should be placed approximately 5 5/8 inch up from the butt (lower) edge for standard size 5 inch exposure shingle, or midway between the 5 inch exposure and the tab sealant strip. You should never nail in or above the tab sealant strip.
- 2. Because I live in Western Pennsylvania, an ice dam protection membrane is required. The code reads: In areas where the average temperature in January is 25 degrees F. (-4 degrees C.) or less or where there is a possibility of ice forming along the eaves causing a backup of water, an ice shield consist of at least two layers of underlayment cemented together or of a waterproofing membrane, shall extend from the eave's edge to a point at least 24 inches inside the exterior wall line of the building. NRCA recommends the ice dam protection membrane extend up an additional foot on roof slopes lower than 4 inches in a foot.
- 3. Lack of an addition layer of felt. On roof sloops lower than 4 inches in a foot, double layer of felt underlayment is required. The felt should be installed "shingle" fashion.
- 4. Asphalt roll roofing shall not be installed on slopes lower than 1 inch in a foot.
- 5. Side wall flashing: Flashing against a vertical sidewall shall be by the step-flashing method.
- 6. Side wall flashing must be counter-flashed. If you would like to know some of the problems I see that don't meet the industry standards and/or the manufacturer's specifications, please let me know. Although some roofs meet the code, they still pre-maturely fail because they are not properly installed.
Michael H. Lichy - RC Lichy Associatesemail: m_lichy@nauticom.net
website: http://www.nauticom.net/www/roofing
I am a general contractor with friend in insulation business. A builder told him to install Styrofoam baffles above r30 hi density kraft batts...with 2x8 ceiling joists. He asked me if this was within code. I said...don't think so...first r30 is compressed in 2x8 space, 2nd the baffles are moisture barriers in themselves and will not allow much moisture to migrate to the "vented space" the baffles provide. I told him the joists should have been larger or at least expanded by a 2x4 nailer crossing the joists below the sheathing....M.K. Garrett <murphy01@cris.com>
A...Michael H. Lichy
In Paragraph 806.3 in the CABO Code reads:
806.3 Vent clearance. Where eave or cornice vents are installed, insulation shall not block the free flow of air. A minimum of 1-inch (25mm) space shall be provided between the insulation and the roof sheathing at the location of the vent.
Styrofoam baffles will assure that you receive the 1-inch space along the eave. The baffles will also allow you to insulate where otherwise you wouldn't be able to, because the space under the roof sheathing decreases at the eave.
You may not substitute a vapor barrier for proper ventilation. You may only reduce the amount of ventilation when a vapor barrier having a transmission rate not exceeding 1 perm is installed on the warm side of the attic insulation. When there is space under the roof, venting of the attic will; reduce heat buildup, provide escape route for moisture and in cold climates, help prevent ice dams from forming. Paragraph 806.2 in the CABO Code talks about minimum free ventilating area.
I believe R30 fiberglass insulation is approximately 9 inches thick. (please correct me if I am wrong). If I am correct, R30 insulation between 2x8 rafters will not allow proper ventilation. This does not meet code. Lack of proper ventilation will cause the roof system to prematurely fail, it will also trap moisture between the ceiling and the underside of the roof sheathing resulting in deterioration of the building products (roof rafters, underside of the roof sheathing, the ceiling and all other related building components)
Michael H. Lichy - RC Lichy Associatesemail: m_lichy@nauticom.net
website: http://www.nauticom.net/www/roofing
(Newsgroups: alt.building.construction) On to a physics type question...I understood that water condensation will occur whenever the dew point was reached. Since there is a temperature gradient within the insulation...if there is moisture from any source (transmitted from inside the house OR in the exterior air from the soffit vents)....it would condense within the insulation where the temperature was at the dew point. Like the iced tea glass...During summer AC...90% humidity in outside air (and attic space)...don't we have some condensation? Do we need to dispurse this? If so...how? with the limited ventilation I described and the addition of a lo-perm styrofoam baffle... murhpy01 <murhpy01@concentric.net>Sun, 30 Mar 1997
The dew point is dependent on both temperature and humidity (with pressure being constant). Warmer air can hold more moisture. So if the house is warmer on the inside (with the moisture barrier on the inside of the insulation), cool air from the outside will be warmed next to the house and it's ability to old moisture will increase. No problem with condensation there . Condensation is a problem of warm wet air being cooled below the dew point.
If the house is air conditioned and is cooler than the outside, then you have a problem because the warm wet air will be cooling inside of the insulation. ...just like the glass of ice tea in warm wet air. There is differences though. There is a much greater temperature differential with a glass of ice tea which is at 32 degrees F sitting in 85 degree air. A normal air conditioned house is at 70 to 80 F with outside temps at 100 degrees (maybe 115 in dry climates) so differential there is only 20 - 30 degrees. In cold climates where the house is warm and the outside is cold, you get differentials as great as 100 degrees and with cooking and bathing inside the house, that air can be very wet pproaching 100% reletive humitiy at times. The "rate" of condensation can be very high.
I don't know if you need moisture protection for AC spaces in warm wet climates since I've never worked in such a climate. I don't think it is a problem to the degree that a warm house in a cold climate is. And besides, with a lower teperature differential, the R value of insulation is not as important. I can imagine condensation in warm wet climates being a serious probem in some instances though. Neal C. Wickham<nwickham@highfiber.com>
Does anyone have suggestions on how to vent rafter spaces in a house with a flat roof? The house would be a pure rectangular prism. No overhangs. No eaves nor eave vents. >Any clever ideas on how to a obtain code-required vent area of 1/150 roof area, as well as adequate cross-ventilation?
All that I can think of is mounting vents on top of the roof, and then placing ceiling joists 2 inches (or so) below the rafters (which would be tapered for drainage). Batt insulation could then be placed between the ceiling joists and you would still have unobstructed lateral air circulation in the space between the rafters and the ceiling joists. But without the benefit of eave vents providing cross-ventilation, would this system work?
Would it work for what? The only criteria you have stated so far is meeting the code, and if you put non-functional vents in, it will do that. The 1:150 rule is a very stupid generalization which does not take into account such rates in various configurations.
The first question is what are you venting FOR? It is possible to build sealed, unvented roofs that work well. Venting is often used to avid, or minimize, ice dams at eaves, ( in which case you are venting cold air INTO the vent space, or thermal venting ) but you are not planning an eave. Venting can also allow moisture that builds up during the heating season to dry out during the warm months, (in which case you are venting dry air to pick up moisture, or moisture removal venting) but if you build a tight interior than the amount of vent. required to do this is minimal, or drying could even take place back into the interior depending on the system. In very cold temperatures air is incapable of picking up any significant moisture anyway, so venting for moisture removal is seasonally ineffective.
Building Science and moisture management have few simple answers, and to give a blanket response is to risk being wrong for the situation at hand. The general rule is to build the interior tighter and more vapor impermeable than the exterior, so the 1:150 rule should read: 150 square feet of vent for every square foot of leakage area into the attic or ceiling. This ratio must be adjusted for the R-value of the insulation used; a more insulative ceiling has more potential for condensation. The solution here is not more vent however; it is a more air-tight ceiling. So my contribution to the debate is the concept of an Air-tightness to R-value ratio: if you add more insulation, you must also air-tighten proportionately, or you risk moisture problems. If codes want to mandate something, they should mandate that!
I want to point out that the above comments refer to a heating climate, in cooling climate much of this logic is reversed!
There is info on roof ventilation at http://www.obdyke.com. If you don't get the answer you want, call Rob in Technical Support - 1-800-346-7655. He'll get you the answer.
Subject: attic venting
Date: 23 Sep 97 13:35:30 GMT
From:
"RC Lichy & Associates" <rc_lichy@nauticom.net>
Newsgroups: alt.architecture, alt.building.architecture,
alt.home.repair, misc.consumers.house
Frank,
If possible, I believe the best method of venting an attic is with continuous eave and ridge vents. That is considering the initial cost of material, the airflow, the long term cost which includes maintenance and cost of electricity.
However, a lot of times the design of the attic space and home does not allow this. For example: I cut-up hip roof with no overhang. Very difficult to achieve proper airflow. You may need a power ventilator in this situation to achieve the proper airflow to remove moisture and heat built-up in the attic.
There are many different methods of venting an attic. I believe each building is different and must be looked at as different. You need to take a lot of things in consideration when designing your ventilation system.
If any one has any additional comments, please email me at m_lichy@nauticom.net. I enjoy good discussions and learning more every day.
Michael H. Lichy
RC Lichy & Associates
Roofing & Waterproofing Consultants rc_lichy@nauticom.net
http://www.nauticom.net/www/roofing
> I'm in the process of getting my attic "made over"
to useable space. > I have a copy of a pub from the PA dept.
of energy or some such entity > and it clearly recommends not
to use attic fans or similar powered units > as there are products
available which will adequately serve the purpose > without
the need to use more power. I have followed its guidelines and
> installed ridge and soffit vents. > I see many posts here
suggesting and recommending the use of attic > fans. Are they
overkill? I feel my vents will be adequate and an attic > fan
will offer no improved performance over what I have installed.
Will > time tell? Are they used on "problem" roofs?
I've seen them on more > low-sloped roofs than my higher, hip
roofed house. Again, my vents are > installed and currently
exceed (slightly) the recommended ratio of > venting/floor
area. Any and all comments are welcome. >
> --
> Frank
>
> "I'm a real boy!"
> - Pinocchio
> ***************************** > F.X. Kranick, Jr.
> CAD Drafter/CAFM Administrator > University of Scranton
> Scranton, PA USA
> kranickf1@uofs.edu
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