I have some window well covers that are blowing off. I could put that savings in the market, an extra mortgage payment etc Rafter Ties Rafter ties are designed to tie together the bottoms of opposing rafters of a roof system. Collar ties must be placed in the upper third of the roof to be properly used. This helps brace the roof framing against uplift caused by wind. If I can get more power generated and lower my electric bill that would be great. Collar ties are designed to tie together the tops of opposing rafters. So far it's pretty cool (no pun intended). I don't live in a historical district and frankly I don't get much for sun actually in the house. My main cringe would be defacing its roof with panels.Įh. A 1900s house is much more likely to be over engineered than a new one and capable of handling the additional load. As for the weight of a solar panel? it is minimal compared to wind loads and snow loads.
If they are solid, the form will resist most anything.Ĭreating a truss or cripple that halves the rafter length, loadwise, is quite good, but generally adds to the load on any central load bearing wall, unless properly designed. The key to strength in any triangle is the strength of the junctions at the apexes. Since the triangle is stable, the effective length of the rafter(s) is only the distance from the birds mouth to the collar tie, making a rafter of small dimensions have the strength of one that is much more robust. Collar ties provide additional structural support for wood-framed roofs that bear the weight of clay or concrete roofing tiles. Downward load at the apex of the roof would transfer equally to both bottom corners of the triangle. The failure point would be the section of the rafter outside of the triangular shape. Pressure on the collar tie going sideways will want to push the entire rafter and tie, and the rafter on the other side of the "roof." Pressure downward at that point will pull at the tie, trying to make it longer, which then will then instead pull the junction at the other end of the tie inward, which is resisted by the rafter on the other side of the roof. Imagine a roof section made of toothpicks glued together, and then a finger pressing in various ways against the construction. Primarily, a collar tie works as a response to wind load.Ī collar tie DOES create a limited resistance to downward loads. Deflection of one side of a triangle is minimized, and since a side cannot change in length, it creates a stable form. A chord is a geometric term, or one used in music to denote relationships between notes.Ī collar tie creates a triangle. Your best bet would be to get all of the specifications/weight on the panels and then have a engineer review the existing conditions to determine if additional framing work will be necessary.Ĭhord, not cord. If it is necessary to strengthen the rafters, you would need to add to the ceiling joists and then add cords or a cord at center span of each rafter which would dramatically shorten the span of the existing rafters adding to their strength. Held fine until we tore it off for a second story addition.Collar ties do add to the resistance of the rafters and walls laterally (to spread) as mentioned above, so they basically are not necessary since the ceiling joists provide the same function. I jacked up the roof over a couple weeks, nailed the out of the rafter/rafter tie lap, and created a truss system with plywood gussets. I talked to my engineer and learned that the connection of the rafter ties to the rafters where they lap was very important. That wasn't enough and over time that nailed joint began to fail and the ridge sagged, the walls moved and the fascia bowed under the stress. They were probably enough to keep the rafters in place, the ridge board from sagging and the walls from splaying outward but the framer only used a couple or 3 16d's at the lap with the rafters. My current house had a concrete tile roof with 2 x 6 rafter ties every 4 ft. Always use the metal straps over the ridge. I've installed engineer designed collar ties with no rafter ties or ceiling joists but they were engineered carefully and installed properly. They might also reduce the deflection on very steeply pitched and undersized rafters in an existing structure. While collar ties are used to resist ridge uplift caused by wind loads, rafter ties.
The author neglects to consider the main purpose of the ties, which is to keep the rafter tops spreading during wind uplift, but this is done much more cheaply through metal straps. Even though they sound like they have similarities, they are very different.
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