Tag Archives: mold growth

Dear Pole Barn Guru: I Have a Roof Mold Problem

ADDED BLOG DAY!  Due to a large volume of questions to the Pole
Barn Guru, we are adding another day for answering questions – so look for more Pole Barn wisdom from The guru on Saturdays – starting – today! 

Welcome to Ask the Pole Barn Guru – where you can ask questions about building topics, with answers posted on Mondays & Saturdays.  With many questions to answer, please be patient to watch for yours to come up on a future Monday or Saturday segment.  If you would like a quick answer, please be sure to answer with a “reply-able” email address.

Email all questions to: PoleBarnGuru@HansenPoleBuildings.com

DEAR POLE BARN GURU: Have a 45′ wide x 120′ long by 20′ tall pole building.  All walls are insulated and covered with plywood sheathing.  Bottom cord of all trusses also sheathed with 1/2″ plywood.  Metal roofing is installed over felt paper that is installed over 1/2″ plywood roof sheathing.  Building has continuous ridge vent and multiple 10″x20″ soffit vents.  None the less we still have mold growing on the bottom side of the roof plywood. Here in Oregon we get ALOT of rain, so frequent moisture issues.  Should I add gable end fans?  Roof fans?  Thoughts. RAINING IN EUGENE

DEAR RAINING: Provided the underside of the ceiling plywood does not also have mold growth, then the moisture is an issue from the enclosed attic space. By Code, the requirement for attic ventilation is for 1/150th of the area of the attic to be in vents, provided at least 50% is in the upper ½ of the attic and at least three feet above the eave vents. This net free area is to be equally divided between the eave and the ridge.

In your case, the minimum requirement would be 18 square feet at both the eave and the ridge. My guess is your ridge is inadequately ventilated, thus the mold issue.

You should begin by replacing your current ridge with a product such as the Klauer Roofline Ridgolator 4 (www.https://klauer.com/metalcomponents.html). With 220 net square inches of free air per ten foot section – your 120 foot long ridge would provide just over the bare minimum required for proper exhaust.

Powered exhaust fans in each gable would certainly help, provided they are located towards the peaks of the gables, and have sufficient capacity to be able to pull air from 65 feet away.

DEAR POLE BARN GURU: What is the depth i should place my poles in the ground in concrete 24×48 10 feet tall not in city. SOMEWHERE IN SNOHOMISH

DEAR SOMEWHERE: As the county you are building in requires Building Permits for all structures the size of yours, and they do a structural plan check prior to issuing permits – you will need to go by whatever is on the approved plans.


Not knowing your design wind speed and exposure, dead loads on the building, roof slope and soil bearing properties, I can only say typically I would expect holes 40 inches deep, with the bottom 18” backfilled with premix. In the event you are constructing a “pavilion” style (all walls open), then it would be best to entirely backfill the holes with

Green Lumber vs. Dry Lumber

Green Lumber

Need a piece of lumber? In most of the United States, you get one from your local lumber yard or “big box” store and do not have a choice as to whether the lumber is “green” (moisture content of over 19%) or dry. For the most part, what is available at the retail level is a regional dictate.

Historically, the green vs. dry battle has been a point of contention.

A great deal of attention was given at the Forest Products Laboratory in 1946 to problems arising from the use of green lumber in building construction. Sharp controversy developed between the Laboratory and that portion of the lumber industry which customarily manufactured and shipped unseasoned (green) lumber.

The statement, since widely quoted, “we still have not learned how to build good houses of unseasoned lumber” was made in a Laboratory report which was later withdrawn. An extensive “Program to Reduce Use of Green Lumber in Housing” was planned at the Laboratory, but never implemented. Although size standards were not a major part of the controversy, shrinkage in service was given as the principal drawback to the use of green construction lumber, thus emphasizing the relation of size to moisture content.

At about the same time was the case of the home owner in Virginia who sued for damages resulting from the use of green lumber in building his house. The court awarded him some $8,000 damages, but the award was set aside on appeal to a higher court.

There was also sharp controversy about whether or not building codes could legally set maximum moisture content values in lumber used in building construction. The argument was advanced that health and safety do not require dry lumber, and the building law could not go beyond health and safety requirements.

You may ask… why is green lumber even used? It is less expensive to produce green lumber than dry. Green lumber is softer than seasoned wood, it can be cut more easily, is not as likely to split and nails drive into it more easily.

A number of problems can result from the use of green lumber. Nail “pops” – as framing members dry and shrink, gaps are created between nailed together framing members, as well as between exterior or interior sheathing and framing members. Mold can begin to grow on green lumber before it is even used in construction. Airborne mold spores are found almost everywhere, and they can easily cause mold growth on wet wood surfaces.

In exposed areas, green lumber can be difficult to paint or stain, sap within the wood oozes out and causes discoloration and gaps between members (such as fascias) can result.

As it dries, wood shrinks considerably, and is prone to both “warp” and “check” (crack). Used in construction, problems may arise including warping the underlying structure and causing structural instability. Unlike lumber which has been dried at the mill, green lumber has not been treated with any substances which are designed to promote water and insect resistance. Green lumber is more subject to rot, and it can be viewed as a buffet by insects.

More often than not, the use of green lumber for framing material comes from lack of knowledge by the end user. For buildings where the finished quality makes a difference, dry lumber is the only sensible choice.

To receive more pole building tips and advice subscribe to the pole barn guru blog!

Water Your Lawn, Not Your Lumber

Lumber is considered to be dry when it reaches a moisture content of 19% or less. When below this threshold, it becomes relatively dimensionally stable.  More importantly, it is naturally resistant to mold and other fungi which will attack wood. When lumber is rained upon, or allowed to sit in mud or puddles, it can gain moisture to above the “dry” point. In as little as 48 hours after getting wet, mold can begin to form on lumber. While a small amount of mold will not usually have an effect on the strength of the lumber, the stains are unsightly.

Green Lumber

Green lumber ready to be dried

Ideally lumber is used promptly after delivery. Otherwise, store in a cool, dry location, avoiding direct sunlight and preferably indoors where humidity variations will be minimal.

Unlike green lumber, keep kiln or air-dried lumber away from moisture, or product may lose the value added by careful seasoning. Dry lumber which becomes saturated with water, such as from rain, melting snow or contact with wet ground, can lose dimensional stability, warp and otherwise deteriorate. Lumber exposed to alternate wetting and drying will check, split, warp and discolor.

If stored outdoors, keep dried lumber off the ground and protected by paper, wrapping, tarpaulins, or canvas. Paper wrapping offers short-term protection.  If it gets torn, repair immediately. Dilapidated wrapping which holds rainwater may increase moisture regain more than if the lumber had no protection.

Air flow is the most important factor in outside lumber storage. Allow large volumes air to circulate freely around stacked lumber in order to evaporate moisture from the lumber. Provide an open storage area with no trees or buildings blocking air flow. Remove weeds, grasses and other vegetation around lumber as they harbor insects and fungal spores.

Good water drainage in storage area is important. Standing water adds to humidity which increases mold and stain possibility on lumber.

When lumber is stacked on stickers (also known as dunnage), place stickers in perfect vertical alignment with one another. Otherwise, sagging will occur. Solid stacked lumber is often stored in packaged units bound with tie straps (or banding) for easier handling. Separate stacked units by spacers, usually at least 4”, and aligned with lower stickers to prevent sagging.

Storing lumber under a roof offers better protection by keeping material dry and bright.

Mold growth on framing lumber is common. To retard or eliminate growth, spray with a borate solution, which is nontoxic to mammals, but highly toxic to most wood fungi. Termites also have a distaste of borate treated lumber.

Following these simple steps can greatly reduce problems caused by allowing moisture to infiltrate and ruin what once was, beautiful lumber.