Hey all,

How strong is a 16' 4x4 beam with one 16' 2x6 board on either side. It looks like an H with a line on top.

I'm putting in a pergola over an existing patio that is 14x10. I don't really want support beams in the middle, but obviously I need it to not fall over.

I've not built anything like this before, just cabinetry and a fish tank stand/hood, so I'm not familiary with support concepts... other than just common sense...

I suspect, very heavily, that if I don't have a support beam at the middle it would fall after I put the cross beams on top, but I was thinking that putting the 2x6s on the outside would make it capable of supporting more weight

Will a board-reinforced 4x4 support the roughly 30 or so 2x6s I'm using as cross beams?

I really don't want mid beams, it will mess up the koi water garden I'm putting in next to the patio.

Not if it's 16' long.

Any span only supported by just two points at the ends is a bad idea. While it will not 'fall down' what it will do is sag over time. The structural ideal is to have at least three points of support. With this if one half tends to sag then it would have to lift the other half. Since both halves are under the same load, they support each other.

Since you need an open span then you have to go with a much taller support than an H-beam made from 4x4 and 2x6. If larger dimension lumber makes for too heavy a look, perhaps you can make a truss or a cable supported beam to take the load.

But if you try spanning 16' with a 4x4 and 2-2x6's, it will sag even without those other 30 2x6's on top. We just finished a similar sounding arbor project. 16' spans that were supported by three cedar 4x10's.

Ok, so here's my design with the support beams in place. The back one is right in the middle of my pond... but whatever.

Jaybee, looks like a great pergola.

From the photo, the 16' boards seem to be slanted instead of fastened at right angles to the supports. If so, could you offer some insight on the reason? Is it for rainwater runoff?

I'm not questioning the logic, just wondering as I'm thinking about building something much smaller to put in front of the West windows to help block the summer sun. I was thinking about lattice on the top to support vining flowers. If it would need to be slanted away from the house, I'll have to change some aspects of my design.

Thanks!

This message has been edited. Last edited by: GardenSprite,

it's my opinion, and I stress "OPINION" that 4 1X4's laminated together with the grain direction alternating is stronger than 1 4X4 because in the 4X4 all grain will run in one direction and a weak link in the beam is carried through the the entire width. However , with a laminated beam each laminate supports the next as long as the grain doesnt run in the same direction.If I were making this pergola I would skip the beam in the pond , but increase the size to a laminated 1 X 8
Of course, the boards must be glued and bolted or screwed together also
Again, " my opinion"

This message has been edited. Last edited by: nona,

quote:

Originally posted by GardenSprite:
Jaybee, looks like a great pergola.

From the photo, the 16' boards seem to be slanted instead of fastened at right angles to the supports. If so, could you offer some insight on the reason? Is it for rainwater runoff?

I'm not questioning the logic, just wondering as I'm thinking about building something much smaller to put in front of the West windows to help block the summer sun. I was thinking about lattice on the top to support vining flowers. If it would need to be slanted away from the house, I'll have to change some aspects of my design.

Thanks!

First off, that was a pic we took prior to it being finished. There is a 1x8 cedar band all around the perimeter plus the remainder of the slats on the right have been added.


Our pergola is there for shade from late morning through afternoon. The slant to the slats is to allow the morning sun to shine through and hit the deck area. Morning sun when it's cooler = good, afternoon sun = not so much.

We tracked the typical sun path and incorporated it into the design.

I don't think you can call a 1-by-anything structural. maybe if you fully glue and laminate under pressure a bunch of them, as in a plywood sheet. but with the usual lazy-J adhesive run and nails or screws, there's too much tendecy to warp if you put load on their sides.

there is the possiblity in the questioner's design that if a couple of A-braces are built from the sides, pointing up, to support a center beam, that it might provide enough structure. act like sailboat bracing. but I think looking at this like you can't put enough angle to them to transfer to the middle of the posts, and the posts are probably not strong enough, and it won't work here.

need two more posts is the short answer, to hold a center beam through the long side. which hoses up the water feature.

or... you can pull the whole design forward of the water feature, put in 6 posts and if you have wind perhaps a good idea would be upgrade them to 6x6, then put three beams across, and extend the shade section free-air over the water feature.

Thanks, Jaybee. Imay change my design plans to incorporate that concept. I want to block the summer sun but not the winter sun.