Gluelams or traditional beams for outside use?

[dresslered]

Hi all,

Seems we have a difference in opinions going on here. I am building a fairly extensive deck and due to snow loading, I had to submit engineered drawings. My contractor and I specified traditional Doug Fir #1 beams, but the engineer called out gluelambs. In the end, he provided the calculations for both so now I have both options to choose from. I always thought that traditional lumber looked better and held up better to weather. My options are:



1) 5-1/8" x 10-1/2 glb (cheaper and smaller)

2) 6" x 14" Doug Fir #1 (traditional big stick, expensive, looks cool)



Both beams will be covered with waterproof membrane on top. Any opinions?

TIA.

David

 

[p-Bar]

either case be sure to seal the end grain with a good varnish that's where it splits.

 

[dresslered]

either case be sure to seal the end grain with a good varnish that's where it splits.

Thanks p-Bar, that is an excellent idea.



David

 

[p-Bar]

Although I am in So Cal I would probably do my framework in structural steel just see too many problems with termites. Would you be using Trex or some other synthetic ?

 

[dresslered]

I'm using pressure treated timbers, powder coated iron railings, and TimberTech Earthwood Evolutions plank. The TimberTech is a little pricey, but seems to have less reported problems than the Trex. We have weird weather in Calaveras County. Very damp winters and dry summers. Tends to make just about everything get a black mold on it. Hopefully, I've found the most maintenance free solution.

 

[Hoefler]

I use glue lams that are treated and rated for outdoor use

 

[p-Bar]

Sounds like you've done your homework.

 

[GHarman]

A small detail

Drape a sliver of "ice/water shield" over the full length, on top, of each horizontal joist or beam under your deck, under the planking. Allow the sliver to overhang about an inch or two on each side, depending on the level of rain you expect to handle each year. The "ice/water shield will protect the joists from slow deterioration due to standing/trapped water. Trex planking or equivalent is great stuff. GregH

 

[dresslered]

GHarman,

Definitely no small detail. Have that specified on the plans. Thanks,

David

 

[dresslered]

Hoefler,

I don't know where my previous reply to you went, but here goes again:

Are these a special spec'd gluelam? How are they holding up to the elements. Do they look allright--we are also doing a stamped concrete patio 12' below and I want the underside of the deck to look fairly decent.

 

[Hoefler]

The look like there inside cousins, except they have a green tint to them. They can be painted. When they are built, they are held to very tight tolerances and engineered to the span, cantilever, and intended load. Using #1 Fir, they are not all the same size and are not rated for outdoor use. Treated lumber is made from a yellow pine, it is stronger than Fir and will usually span farther. A yellow pine 2"x10" will carry the same load as a 2"x12" fir in the same span. Even if you cover the top of your beam, it will draw moisture or condensation, the cover will make it last a little longer, but you will still get dry rot. If your not having a drip guard system installed, the underside of you decking, Trex for example, is not very pretty on the bottom. Also, if you are going to use a composite decking, joist need to be on 16" centers, 12" if you are running them on an angle.

 

[dresslered]

Thanks for the info Hoefler. I need to question the engineering calcs as he is claiming that I can only run 9' 8" spans with these beams. Seems a little overkill. I will check out the local lumber yard. If I went with the traditional lumber, I was going to use pressure treated for all.



Also, I had spec'd 12" centers where I would be running the diagonals but the engineer said that the TimberTech could handle all 16's regardless if it was diagonal or perpendicular??? I hadn't heard that before.

 

[Hoefler]

Timber Tech states in their installation literature 12" on center for diagonals. I would get a different engineer. I deal with this stuff quite often, matter of fact I have 3 new decks to build in the next 8 weeks.

 

[JLEONARD]

I did my deck with pressure treated. Span called for 2x8, I used 2x10.

Covered with the textured Trex. Called for 16 on center, I used 12.

Also 2 extra support columns in case I want a future hot tub.

The deck is solid as heck. The grand kids jump rope on it and it doesn't move.

Better to overbuild.



Then to hide the 2x10 end beams I applied facia stone. Deck is close to the ground so it looks (at a quick glance) like the deck is built on a stone wall.

 

[dresslered]

Thanks all,

We straightend out the drafter today. The TiberTech is 12" for 45-degree diagonals and 14" for 30-degree diagonals. The new Earthwood series looks like a board with no difference on either side so will look good from below as well. It also uses a hidden fasterner system. I wish I could post a pic of the plans but they would show up too small. Existing 40-year old deck used 4x8" main beams. New codes have required me to go to 6x14's (unless I go for the gluelams) to accomodate a fluke wind from unloading the snow load on the roof to the deck (the roof doesn't even slope this way). I guess if I need to park my truck on it, it will hold.



The biggest reason I had to go through all this engineering is I am building next to the septic tank (just as the old deck had done). New code is requiring me to get a variance and a special 'key' built next to the septic tank. This 'key' (6+ foot underground retaining wall) is like building the great wall of china underground to protect the tank from lateral forces. Addtionally, I opted not to replace the lower deck that had been there before. It is getting replaced by a raised stamped concrete (grainite look) patio.