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Eliminate Moisture Penetration from Butt Joints with Belco XT® Exterior Trim and Fascia

exterior trim and fascia

Moisture, whether condensation or rain, can sneak through a butt joint, and become a concern with exterior trim.  In fact, moisture penetration into any part of the building’s envelope surpasses concern and can impact builder liability.  It has become such a serious issue, that some builders sheath their exterior walls with moisture resistant OSB. They then add house wrap. This is all in hopes of containing a mishap that could turn into millions of liability dollars.

Installing Butt Joints with Exterior Trim and Fascia

Exterior trim butt joints can be an avenue for moisture to get behind the trim.  When cementitious, or OSB trim, is installed on a home, it requires a butt joint with a minimum 1/8” gap. This gap must be caulked, hopefully with high quality caulking.  This joint is necessary because these products expand and contract at a much different rates than the studs and sheathing, they are fastened to. Joint expansion happens most during times of temperature change. Which is usually during the transitional seasons of fall and spring.

The structural framing of the building expands and contracts at different rates. So, if these products didn’t call for spacing at the butt joints, they would likely crack. This could lead to yet another potential moisture penetration. The different rates of movement between the structural framing, and the engineered or cementitious siding trim can also cause the butt joint to separate from the caulking. This can open-up an avenue of moisture penetration. These butt joints offer the least protection of moisture intrusion of any joint. But, they are also just ugly to look at. Additionally, they offer diminished curb appeal at best.  This applies not only to siding trim, but also to the fascia and barge as well when a two-piece construction method is used.

Two-Piece Exterior Trim and Fascia

A “two-piece” fascia and barge consists of a structural fascia/barge fastened to the rafter tails and outriggers. This is typically a non-treated 2×4 or 2×6.  This non-treated board is then covered with engineered or cementitious trim to provide the finished, appearance grade look. This can cause two problems.  First, engineered, and cementitious products are often revered for their stability. However, in a barge or fascia application, they are only as stable as the structural substrate they are fastened to-typically hem-fir, or southern yellow pine. Neither are praised for their stability.  When the structural portion of the framing eventually begins to twist, it causes the beauty board on top to do the same, this separates butt joints and cracks caulking, allowing for more moisture intrusions.

The second issue is the length limitation offered by these engineered and cementitious products.  With only 12’ or 16’ lengths there are a lot of butt joints around the perimeter of the roof line that can possibly open when the structural substrate starts to move.  Some of these will be hidden behind gutters, and partially protected if the gutters remain clean, so they don’t overflow. But any joint of the barge has the same potential to open up and be a real eye-sore on top of being a potential water penetration point.     

Belco XT® Exterior Trim and Fascia Requires Fewer Butt Joints

There is a great and simple solution to this problem.  It is Belco XT® exterior trim and fascia.  Belco XT® Trim and Fascia comes in multiple lengths from 10’ to 20’ in 5/4 and 2” material.  What this means is far less butt joints, and with 20’, possibly NO butt joints on the exterior corner trim, or the barge. As a reminder, the barge is the trim most exposed to the elements, and visible from the curb.  Unlike its engineered & cementitious competitors, Belco XT® exterior trim and fascia can be cut with a scarf joint when needed. This produces a much cleaner looking joint that is far more moisture resistant, especially on a vertical trim application. This is because the angle of the scarf should be sloped down to inhibit moisture from penetrating the joint.

Since it is wood (SPF) with a full preservative treatment under the primer, it is easier to cut and install.  Additionally, the weight of Belco XT® Trim is about half the weight of most engineered trim products. The multiple lengths allow the sider to trim more homes per day than when using engineered trim.  A happy sider produces a better installation, but the builder benefits the most by having a cleaner and aesthetically pleasing product, that also provides far less liability!  Belco XT® Trim is growing, and has, or will, become the exterior trim of choice for many large and small builders.

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