I installed some Composite Lap Siding from Home Depot today to replace some Vinyl Siding that was breaking up. I only did one small short wall, but I’m thinking about doing the whole building and was wondering how it butts together on long walls.

I saw a video of a different brand of siding that had plastic butt connectors, but Home Depot doesn’t carry such a thing. I figured I would have to use flashing behind the joints, but it says to leave ¼” space between them.


I posted this question on another site, but the site went haywire and I can't wait for an answer because I want to start planing within the next couple of days.

I'm pretty sure they just but against each other.....I've seen a few houses and there were no connectors...

I just have a problem with the exposed 1/4" gap which I do believe is needed. I once did a 30ft wide roof with 1/2" plywood underlay and I did not leave a gap. That was a big mistake because as soon as the summer heat hit it, the whole roof buckled.

The lengths just butt together end to end. I don't know how regular installers do it but what little I did I covered the wall with felt paper first and put a bead of caulk on the end of the board where the seam was.

It depends on the composite material. If it's a petroleum product, such as a composite plastic, or even a composite wood, there will be some thermal expansion. However, if it's a cementitous composite product like HardiePlank, no worries with movement, and no need for a gap.

right....the stuff i've seen was concrete based....and did not have gaps.

FWIW, Hardie does recommend flashing beneath butt joints. I don't know anything about this composite siding, but to me it makes sense to flash at the joints regardless.

You linked to an LP composite lap siding product. You can get the installation instructions, here. http://www.homedepot.com/catalog/pdf...50c49da8d3.pdf
This type of siding is not used or available in my area of the country. "joint moldings" are available from the manufacturer, you need to talk to the contractors desk, most floor people in the big boxes don't know much.

I guess rain and snow aren't frequent occurrences in your neck of the woods. They are where I am. These conditions would make the LP product buckle. They recommend a 3/16" gap when butting at a joint, window, corner board. Then a high quality flexible caulking is used. That's a fair size gap to fill, it may have to be done in more than one application. If you do experience humidity changes, the caulking may need frequent maintenance. Whether it shows would depend on how well the caulking was done and how much the siding typically will move.

Some installers will use a small strip of tar paper or bituminous flashing at butt joints. In the event the caulk or joint molding leaks, the strip serves as back up insurance. End cuts need to be primed. The siding should be acclimated to site conditions. Windows, doors and corners should be properly flashed. I've found that ordinary caulkings don't stick well to synthetic trim. I would contact 3M for a professional caulk and order it, it won't be in stock at most places.

This site is on top of a mountain about 7000 ft and we do get snow sometimes drifts up against the building 5 ft high. There are huge swings of temperature changes between night and day so I think the gap may be necessary. I buy caulking for up there by the case because nothing last very long and I'm constantly filling in where the caulk has come off.

I flash behind the joints and use DAP Dynaflex 230 caulking.You do need the gap.

Thanks I've decided that this is exactly what I'm going to do.

I was under impression that siding was overlapped an inch or two, instead of butting the ends to other pieces. Overlapping would not allow and open space between the ends of the siding, therefor not leaving a space for rain or insects to enter. Am I in error of my thoughts?.

Vinyl siding overlaps, composite siding is too thick to do so.

You couldn't over lap this stuff as ryan50hrl mentioned, but also with the width being so wide it would really look bad.

My error, I had in my mind that it was vinyl siding is what was being talked about. I missed the operative word, "composit".

I'm actually replacing the existing vinyl siding with this composite stuff, because the vinyl is breaking apart.