Are the gaps in decking boards (PT or composite) *REALLY* necessary?

[Thomas G. Marshall]

I've spoken to a number of people who have put composite decks in and they followed the manufacturers suggestions carefully and ended up with boards that just "seem" too far apart. A friend of mine has these large gaps around his posts that I'm not particularly fond of.

And two of these people say they've never seen the boards expand nor shrink the way the manufacturer warned. I'm not sure of the brands.

But this reminds me of something a construction guy told me once about PT (I know, a different issue): "Don't ever listen to the advice about keeping the boards a nail width apart....they will dry and shrink on their own". The only reason I mention this is because I would like to know to what degree such rules of thumb (PT or composite) are real, or just passed along advice that never really applies.

For example, has anyone seen trouble with compostite decking boards placed flush (say, in the summer)?

Thanks!

[Wilson]

sometime in the recent past Thomas G. Marshall posted this:

But if already well dried, they will expand on their own too. The

All materials expand and contract. Without spaces, dirt will still find its way in and then stay there, water will puddle and possibly freeze. Sometimes 'been doing it that way forever' has a real reason. Just my 2 cents.

[Dioclese]

Don't know anything about composite.

Treated lumber, like any other lumber, absorbs water. In that process, it expands. As an example, treated lumber placed immediately next to the next deck plank sequentially may buckle. This is because the board expands and may cup either way as well as a result. There is no room for expansion. Would suspect that composite may have the same property if it absorbs water as well.

[Steve]

"Thomas G. Marshall" wrote on 25 Apr

2008 in group alt.building.construction:

1. It's a standard look. If I don't do it that way, some clients will complain.
2. Expansion is a real problem if the wood is already good and dry. If you're using the stuff from the borg that drips when you put in a screw, go ahead and butt it together.
3. Puddling might occur if the boards don't shrink. The contractor doesn't want to be sued because you slipped in a wet spot.

[EXT]

While I find that new PT wood is in various stages of being soaked with water and will shrink in width according to the amount of wetness.

I have found that composite materials do expand, particularly in length, during summer and shrink in winter. I have some 20 foot lengths and they can grow about a 1/4 inch in length over the winter measurements, and they will actually "crawl" or move in one direction over a number of years, requiring some leverage and banging to get them back in place. We do have extremes in temperatures, winters down to zero, and summers up to 100 degrees which can cause these problems.

[JIMMIE]

Composites are spaced for drainage and yes I have seen them spaced too far apart. I think they actually make guage for spacing them now.

[Thomas G. Marshall]

Dioclese said something like:

...[snip]...

Ok. Hmmmm....my side porch (uncovered, and just a landing for steps leading into the house, perhaps 5' x 7', is covered with 5/4 PT untreated, and it was placed tight and never buckled. I'm not saying that this is the rule, I'm just adding it as empiracle evidence that's made me start to wonder...

[Thomas G. Marshall]

EXT said something like:

Huh....Hold on.....please verify.... The composite grows when cold and not when hot?

[Thomas G. Marshall]

JIMMIE said something like:

It really really detracts from the looks I think when the gaps are large. You start looking at a porch or a deck as an ordered collection of gaps, and not boards.

[Edwin Pawlowski]

Re-read what he said.

[Edwin Pawlowski]

"Thomas G. Marshall"

PT is wood. Composites are a mix of wood sawdust and plastics. The movement will be different so you are comparing different physical properties. With wood, most of the expansion occurs in one dimension, the board width. With plastics, it will occur equally in all dimensions.

Other factors are the temperature and humidity swings where you reside and that of others who may take your empirical evidence and apply it to their situation that may differ greatly.

[ransley]

You need some gap , air venting of moist air. there is expansion, and for you, dirt and rain removal . Also an ease of cleaning.