Sorry, another deck question...

[pslamp32]

What say ye is the best way to attach a ledger board to the cinderblock part of the house? The book I'm reading says to use 3 inch masonry anchors to hold lag bolts but this I believe is for solid concrete. Since the blocks are hollow is there a different method? For some reason I feel some trepidation in attaching the deck to the house, like it could weaken the foundation or something. Stupid I'm sure, but since I'm trying to do this myself I'm afraid I might goof up and cause serious damage. That's why i was thinking about digging more holes and making the deck freestanding but that sounds like way more work. Hmmm...

 

[DaveO]

Ideally if you are locating the deck at or just below the floor elevation of the house you would attach your ledger board into the rim joist that supports the floor joist. But if not and you have to attach to the CMU foundation the best bet would be to drill through both sides of the block with a hammer drill and long masonry bit. Fasten the ledger board with carriage bolts or standard hex head bolts all the way through the block and back-up the nut and washer with another board on the backside of the block. CMU block is very brittle and you would run the risk of pull through if you used lead sleeves or expanding masonry anchors. It is best to spread out the load across the widest surface possible. Or go free standing.
Dave

 

[McRabbet]

Peter,

You are right that you do NOT want to use 3-inch masonry anchors and lag bolts on cinder block. The best choice is to build the deck as free standing and put in posts in to support the house side beam that the deck joists will sit on. The joists can overhang the beam (i.e. be cantilevered) up to 18 inches so the posts can be set away from the foundation. You will still have a band across the ends of the joists that will tie their ends together and it wants to be in the same position as the ledger would be, but it does not connect to the foundation.

Your second choice would be to use 5/8" through bolts and sandwich the cinder block between a ledger board on the outside and a similar board on the inside of the wall (the block wall becomes the "cream" in this Oreo cookie!). The city inspector might not approve this, however.

In your plans, be sure to allow for actual lumber thickness for your decking and the joists when you locate the tops of the beams. I make my beams with a pair of 2 x 8's or 2 x 10's (depending on span) that are through bolted to the posts with 5/8" bolts, two bolts per post. Obviously, posts need to be set with their sides at right angles to the beams and aligned in a single plane if there are more than two posts per beam.

 

[pslamp32]

Thanks guys. Hey Rob if you're ever available, do you think you could inspect the site where I want to build the deck and impart some wisdom? You seem to have done this a bunch and I think it would all make more sense if someone could instruct me before I begin. I think I'm leaning towards my initial urge to make the deck freestanding. It would make me less nervous if I mess up. Thanks!

 

[pslamp32]

I make my beams with a pair of 2 x 8's or 2 x 10's (depending on span) that are through bolted to the posts with 5/8" bolts, two bolts per post.

Hey Rob, why this way as opposed to putting the beams on top of the post? What are the pros/cons. It just seems that stacking them on top of the post would be easier.

 

[pslamp32]

Oh, and another question. The permit guy said that the holes must be 18" X 18". Of the 18 inch depth how much must be footing and how much can be the pier? The book also says to put ~2-3" of gravel so that leaves 15"...confusing. Oh, and does the footing have to be the whole 18" in diameter?

 

[FredP]

when i built decks [ years ago ]:roll: hole had to be 18" x 18" x 12" deep with the post on top of the concrete
also your CMU block wall should be filled with concrete. at least the top corse will be. this is where they imbede the anchor bolts that holt down the house. the codes changed soon after all those silly college kids crashed a deck to the ground.8-O anchores are not allowed. deck must be through bolted i believe every 24" or free standing. through bolts are to be 5/8" diameter with washers. at least this is to the best of my recall [ and my recall is sightly broken ]:-( oh and WE WANT PICS!!!!!!:eusa_danc

 

[FredP]

when i built decks [ years ago ]:roll: hole had to be 18" x 18" x 12" deep with the post on top of the concrete
also your CMU block wall should be filled with concrete. at least the top corse will be. this is where they imbede the anchor bolts that holt down the house. the codes changed soon after all those silly college kids crashed a deck to the ground.8-O anchores are not allowed. deck must be through bolted i believe every 24" or free standing. through bolts are to be 5/8" diameter with washers. at least this is to the best of my recall [ and my recall is sightly broken ]:-( oh and WE WANT PICS!!!!!!:eusa_danc

BTW I may have the bolts if you dont need more than a dozen or so. let me know what lenth and i will see if i have em long enough.

 

[Nativespec]

Peter:

You might want to look at appendix M of the NC Residential Code regarding wood decks. If there is no brick veneer, you may use 12d nails as long as they penetrate 1.5" or you may through bolt it with 5/8" gavl. bolts (nails ar not an option for brick). You can cantilever up to 24" if you are building a free standing deck (a great idea if you are attaching a deck to a wood structure). Posts have to rest on a footing (drystack or precast) and the tributary area determines the number of posts. The footing has to be 6" to 8" thick and the bottom will need to be 18" to 20" inches below the frost line (Chapter 4-foundations) and this depends on size of post and tributary area. The girder (has to be doubled) can either rest on top (I use let in's because I like to use the posts for my railing) or bolted with 2 5/8" bolts per post (as mentioned above).


Also, you have to consider table R502.3.1(1) for floor joist spans. You can use 2X2" ledger boards (my preference) or joist hangers for attaching joists to girders.

Another Item: 2x6" is priced (at Lowes) almost the same as 5/4 decking and would be my choice.

You may want to check the library to see if they have a code book.

David

 

[McRabbet]

Thanks guys. Hey Rob if you're ever available, do you think you could inspect the site where I want to build the deck and impart some wisdom? You seem to have done this a bunch and I think it would all make more sense if someone could instruct me before I begin. I think I'm leaning toward my initial urge to make the deck freestanding. It would make me less nervous if I mess up. Thanks!

Sorry I haven't responded earlier, Peter, but today I chaired the December meeting of the Western NC Woodworkers Association (we elected a new Board of Directors for 2008 and had a great presentation by Bob Shuford [Bumout Bob here] on making knives).

The earliest I can come up to Asheville is Tuesday and I'd be happy to review your site plan and help you understand several of the key elements of deck construction. If you haven't gotten a solid plan put together yet, we can sit down at your computer and generate one if you'd like. Just let me know when it would be good to come up.

 

[McRabbet]

Hey Rob, why this way as opposed to putting the beams on top of the post? What are the pros/cons. It just seems that stacking them on top of the post would be easier.

It is much easier to attach the beams my way and I believe it is the preferred way used by most builders because it is more forgiving and plenty strong. It also allows you to extend the posts up to use as railing posts if no cantilever is used. If you are building a large deck with 6" x 6" posts, the beams are even stronger if they are let in to the sides of the post in a notch on each side and then through bolted.

You can place beams (e.g., a 4" x 6" solid beam) atop posts and just toe-nail them to the post, or use metal ties or 2"x4" gussets sistered to the post to form a crotch for the beam to sit in. The posts must be trimmed to an exact height (from the final deck elevation, subtract deck thickness, the joist size and the beam size). If the beam is not dead straight (it never is), it will tend to rock or teeter on the highest post.