Deck spacing near house

[bookman51]

Putting in Trex composition deck boards to replace the old wooden boards. Doing it in 70 to 90 degree weather. How much spacing should I leave between the last board and the siding of the house? Looks like I will have to rip boards to the right width. Could I do a silicone caulk between the last board and the house or should I leave the gap open? Thanks in advance.

 

[pmiranda]

I'd leave at least as much gap as the gap between boards so there's space for expansion, and to avoid wicking water into structure. There should already be something separating the old boards from the house.

 

[tros]

I used the hidden fasteners to do mine and used z channel on the house with silicone caulk it is working well. Its been 2 years now .

 

[tarmy]

Just replaced my 20 year old Trex deck...with the new version...

I repainted/sealed the area of house where the deck was (too close last time and got some dry rot). I left about 3/4” this time...looks great and with heat/cold temp changes allows for movement.

Also, that gap is big enough to paint again in a few years if I need to....

 

[bookman51]

I used the hidden fasteners to do mine and used z channel on the house with silicone caulk it is working well. Its been 2 years now .

Thanks, I am just thinking of something to keep the rain off the wood that is fastened to the house. So, I am wondering if a silicone caulk to fill the gap with would be flexible enough to cover whatever expansion and contraction the Trex composite board has but still keep water from going onto the joists fastened to the house. Thanks

 

[bookman51]

Just replaced my 20 year old Trex deck...with the new version...

I repainted/sealed the area of house where the deck was (too close last time and got some dry rot). I left about 3/4” this time...looks great and with heat/cold temp changes allows for movement.

Also, that gap is big enough to paint again in a few years if I need to....

Interesting...a 3/4" gap between the last composite board and the house siding. Ummm

 

[APEowner]

The deck ledger should be properly flashed and the decking should have a gap for drainage.

 

[Innovate1]

Where the plank runs parallel to the house how do you keep the gap for drainage without a big gap on the top side? I have thought about notching the bottom of the decking to create a path for drainage. There is flashing over the ledger board but the decking is close enough to the house to close the gap.

 

[Dustball]

Interesting...a 3/4" gap between the last composite board and the house siding. Ummm

3/4" is a bit on the large side but fine to me. It allows for leaves and snow to fall down instead of sitting against the siding. I actually ended up with about 3/8" - 1/2" for mine when I replaced it this year. I also built it so it's a full step down from the door. You can see the a bit of the door frame rot from when the deck was flush with the door sill.

 

[nadogail]

I think that 3/4"" is a lot of space, how about 3/8" instead?

 

[rayra]

It's not a carpet. Leave a gap. Better yet don't attach to the house at all, if you can engineer it that way.

 

[yeldogt]

Is the ledger board flashed?

You don't want to use any caulk ...

 

[CraigStu]

I agree, leave a gap. I'd want minimum 1/2 inch and I'd be fine w/ 3/4. I like the idea that rain, snow, etc has a place to go so it isn't just sitting there in contact with the house. I also go for 1/2 inch gaps between all the boards. Our previous house had the deck covered w/ that super thick paint from Behr. It was almost water proof. It was also the biggest pain in the **** to wash off. When the water and loosened **** won't disappear between the boards, you have to hose all the way to the edge, 15 ft away.

 

[Innovate1]

I agree, leave a gap. I'd want minimum 1/2 inch and I'd be fine w/ 3/4. I like the idea that rain, snow, etc has a place to go so it isn't just sitting there in contact with the house. I also go for 1/2 inch gaps between all the boards. Our previous house had the deck covered w/ that super thick paint from Behr. It was almost water proof. It was also the biggest pain in the **** to wash off. When the water and loosened **** won't disappear between the boards, you have to hose all the way to the edge, 15 ft away.

I agree with the gap at the house but 1/2" gap seems way too much between boards. 1/8 - 1/4 should be about right. Ours were installed with barely any spacing and plug up with crud easily. It's the older style with face fasteners. Have thought of running a circular saw down each gap to fix the drainage.

 

[PelicanPines]

Whatever gap you leave... will fill with dead leaves, dead bugs, live bugs, wet, mold. The house needs to be flashed and drainage needs to be ASSURED.

 

[Jackfre]

I would recommend that you use the Camo system for your composite material. I have a small porch and we tried a few methods. The Camo was the clear favorite and 6 yrs later everything looks like new. I'd keep an open space at the building, flash it properly and once in a blue moon, clean out the debris.

 

[bookman51]

Whatever gap you leave... will fill with dead leaves, dead bugs, live bugs, wet, mold. The house needs to be flashed and drainage needs to be ASSURED.

I have all the old boards off. Under the planks is a 2 x 8 board attached to the house. It runs parellel to the planks. It has not been flashed but I do not see any damage. I plan to flash it. Still appears no way for anything to drain or otherwise get out of any gap I leave. And, there has been an accumulation of dirt, etc. in the current gap. I am tempted to leave about a 1/4" so so gap and then fill it in with appropriate colored silicone. I am using Trex composite boards so I do not think there is much expansion and contraction (not like wood anyway). I will have to rip the boards to the right width anyway since a full width board will in fit into the available gap. Anything wrong with that plan?

 

[bookman51]

I agree with the gap at the house but 1/2" gap seems way too much between boards. 1/8 - 1/4 should be about right. Ours were installed with barely any spacing and plug up with crud easily. It's the older style with face fasteners. Have thought of running a circular saw down each gap to fix the drainage.

With mine, the deck is attached to the house. Under the current planks is a 2" x 8" running parallel to the planks. So any gap I leave under the width of the this joist will means water and whatever will run to top of this joists and stay. It is not currently flashed but I do not see any damage. So I plan to flash it. In fasting the new composite plans on top of it, I don't think there will be much, if any room, for drainage of water and certainly not for any dirt and other crud that gets in there. That is why I am thinking of leaving a 1/4" of so gap and filling it in with flexible silicone. I am using composite materials so I would think there is much expansion or contraction (not like wood anyway). Anything wrong with this plan?

 

[pmiranda]

The composite boards might not expand or contract, but the framing they're attached to will. Water/bugs/leaves will find their way into any seam. If the seam is big enough they'll pass through and drain below. Whether you caulk it or not, inspect it once in a while since caulk will get old and crack, and any gap will eventually gather enough junk to clog up and rot.

 

[bookman51]

Is the ledger board flashed?

You don't want to use any caulk ...

As I have explain to others, under the wood planks I have removed, there is a 2 x 8 that attaches to the house. The planks run parallel to it. It has not been flashed but I plan to flash it. It also does not look damaged. However, whatever gap I leave means materials will accumulate in the gap. Plus with the composite planks fastened to it, it might even retard any water from draining out. So, that is why I am thinking of leaving a !/4 so gap and filling it in with flexible silicone. I am going to have to rip the planks since a full width plank will not fit into the gap I have left. I am using Trex composite boards. While there is some expansions and contraction, I don't think it is nearly as much as wood. Anything wrong with this plan or are there better ideas? Thanks

 

[pmiranda]

A picture might help.. are the joists (that run across the deck boards) hung from that 2x8 ledger? Sometimes the joists set on top of the ledger to prevent creating a an undrained pocket. Do your deck boards sit directly on the ledger or are you using a system with spacers?

 

[bookman51]

The composite boards might not expand or contract, but the framing they're attached to will. Water/bugs/leaves will find their way into any seam. If the seam is big enough they'll pass through and drain below. Whether you caulk it or not, inspect it once in a while since caulk will get old and crack, and any gap will eventually gather enough junk to clog up and rot.

Thanks, good points.

 

[Los_Control]

My experience with trex you can rip it like any wood to width, then use a router to re-create the bull nose.

Leave a gap! First deck I built with it, we did our best to keep the boards perfectly spaced, used blind fasteners underneath ... It really looked nice and happy with it ... end of day and ready to go home, we were devastated ... was 90-100 degrees out and the planks looked like snakes.
All we could do is go home and sleep on it, next morning the planks were perfectly straight again.
Just amazing how much the trex expands and contracts with weather .... do not silicone it to the house.