Help me puzzle through my deck attachment...

[Erin]

Our deck is going to be relatively tall, approximately 8' clearance (over a walk-out basement), and run the full 40' of the house's south-facing wall. 
We'll have 2" of poly-iso on the exterior of the wall.   
The south edge is going to be hanging on telephone poles set 10' apart, probably with 2- 2x10 ledgers, inset a bit into the poles, and bolted through to sandwich it.  Cross braced for lateral stability.


It's the house-side that's giving me issues, particularly because it's a post and beam house set on ~4' centers and doesn't have a typical rimjoist on the floor joists.   I could:

1.  Attach a ledger into the posts of the house and run my deck joists over to my south ledger on the poles.
2.  Built a free-standing deck and use something less impressive (6x6 timbers I suppose? or 4x4s?) on the house side and bolt to the house for additional lateral strength.
3.  something else?


Another issue I'm chewing on is, do I want to flash under my poly-iso and over my house-side ledger?  Or do I want to go down both the poly-iso and the ledger with flashing and keep them essentially in the same plane? 
I figure I'll put self-stick flashing under not only the ledger, but also some distance up under the poly-iso as well.  I'm also planning on 1/2" spacer washers to bring the ledger board out into the same plane as the  insulation, as well as creating an air gap between ledger and wall...

[grover]

1.  Attach a ledger into the posts of the house and run my deck joists over to my south ledger on the poles.
I think things will be much more secure if you attach a ledger to the posts of the house, especially with a deck that tall.  I assume the foam board have to be cut away if you attach a ledger?  I'm not able to imagine how that will work.  Will the foam board stick out 1/2 inch more than the ledger?  You can't attach it and sandwich the foam.  Even the spacers that you mentioned will weaken the attachment a little but can work if done correctly. 

Myself, I think attach the ledger to the posts and run your flashing up under the foam and out and over the ledger.

I have a question myself.  If your flashing goes over the ledger won't that eleminate the need for the spacers?

Take my advice with a grain of salt.  As you can tell I am not a professional builder.   

[MountainDon]

If I understand correctly the intent is to secure the house side ledger directly to the wall timber posts, but with a spacer between post and ledger. No insulation between the ledger and the post, and that is very good.  . But I don't know about the spacer/washer being a good idea. That can cause extra bending force being applied to the fastener under loads. I understand the idea is to end up with the surface of the polyiso and the ledger face being in the same plane.  It might be better to obtain a true 2 inch thick piece of lumber for the ledger?   

I'm not an engineer but an engineer cautioned me against doing things that place spacers between the main and side members (main = the post, side = the ledger, in this example). An engineer would be able to calculate the forces and recommend the size and number of fasteners. But with the timber posts being 4 feet apart I have no reliable idea if sufficient strength of fasteners can be achieved.   Deck loads tend to get high and get concentrated as people gather in groups. The loads are often underestimated.



The other thing bothering me is the height. At 8 feet I do believe you are in the zone where, if there were inspections, an engineer would be required. Even without inspections I do believe it would be prudent to have design advise from a PE.


IMO, FWIW.

[Erin]

If I understand correctly the intent is to secure the house side ledger directly to the wall timber posts, but with a spacer between post and ledger. No insulation between the ledger and the post, and that is very good.  . But I don't know about the spacer/washer being a good idea.

yes, it would be directly attached to the wall, before insulation (which is why I'm wondering if I should bring my ledger out into the same plane)
And it's entirely possibly I'm missing something, but how would a spacer like this allow more bending force than just having a solid piece of lumber?
http://www.deck2wallspacer.com/D2W58_Install_Table.pdf

http://www.finehomebuilding.com/item/14656/how-to-attach-a-deck-ledger-to-the-house

[MountainDon]

When you first mentioned a 1/2" spacer/washer all that came to mind was a stack of hardware store washers as there was no mention of what was implied. Those look interesting. They have been put through an ICC test according to what I see. That's good, but does not guarantee acceptance... the phrase "...shall be designed in accordance with accepted engineering practice...." is a sort of a fuzzy catch all... it does not mean the device is actually code approved. It is a step along the way.  If there were inspections the inspector would have to be convinced.   

Anyhow those do look better than what was originally envisioned by myself.   I still wonder how the load trace would work out... how many pounds per fastener you end up with since the timber posts are 4 feet apart.  What size timber posts in the house wall?   


To the flashing...  Is the general plan to have the polyiso shiny foil face outwards? Make that as a weather resistive barrier?  Then I would think any flashing at the polyiso / ledger interface should start behind the upper layer of polyiso, bend outwards over the ledger and over the exterior face of the ledger. Preferably it would extend down to overlap the polyiso below the ledger. But then how are the joists mounted to the ledger w/o breaking the flashing or relying on caulk?     I can't get my head around that... need to think it over...

[Don_P]

Getting late but thought I'd add 2 cents. Mt Don is, as usual, on the right track. The house post spacing is going to exceed the bolt spacing requirements listed in... ahh... chapter 3, first page or 2 I believe. The spacers, any spacers, are going to derated the bolt capacity. In an older JLC article by Dr's Woeste and Bender they give stacked washer reductions. IIRC it should come up in a search for "deck ledger attachment" and their names, it was also in structuremag I believe, a series of 2 articles. I haven't read the info on the plastic spacers but if they don't give test ratings it is going to default to the stacked washer values... which at 4' isn't going to be enough even if no spacer is used. I do agree with tying to the house for lateral but the vertical support needs to come from posts to the ground.

[MountainDon]

Thanks for the clues as to the search terms, Don   


http://www.structuremag.org/article.aspx?articleID=669

Scroll down to the bottom of the article and there is a link to D/L a copy in PDF format. It is easier to read than the online page.

[MountainDon]

Perhaps a related matter can help understand the fastener derating. I don't know what exterior siding is planned for application over the polyiso foam. Fairly common is lap siding over vertical furring strips, over rigid sheet foam over the usual 2x4/2x6 framing and wall sheathing (ply/osb).  Fastenal makes HeadLOK structural screws for fastening the furring through the foam to the studs. As the foasm thickness increases and the weight of the siding increases the number of fasteners also increase. That is because of the bending moment. It is true, in this example that the foam insulation has virtually zero resistance to the bending of the fasteners. But the washers are not that much superior. There is still a smallish friction area between the washers and the two wood layers. They use three screws to secure the washer to one one the wood members, but it's only to one. Most of the load is being applied to the bolt fastener, but the friction between the surfaces may also be involved. Some steel building components use friction between members for their load carrying... that may not mean anything with wood... another case of some partial  knowledge being dangerous and not transferable between different systems.   



FYI the HeadLOK document is located on this page...
https://www.fastenmaster.com/details/product/headlok-heavy-duty-flathead-fastener.html

Look under the Technical Data tab and click on the HeadLOK TER Report.

[MushCreek]

I like the look of these, but they ain't cheap:

http://www.deckbracket.com/

[Don_P]

One other thought, one reason for keeping deck posts 8' or less apart is so that you can weave the plies of the outer rims with typical 16' lumber.

I was mistaken above, the ledger connections in the IRC are in chapter 5, three pages in. The deck2wall spacers do give a little wider spacings than the stacked washers so I'm guessing they must be getting some bump for the screws. Interesting side note, the lab they were tested in is Dr Bender's, from the article above and the development of the code table. I'd say their numbers are good.

The Maine Deck Bracket was developed for brick veneer jobs. Structure is not allowed to attach to veneer so this was a way of getting back to the house frame while projecting thru the veneer to attach a ledger. I'm not sold on these but they do have an ESR, do read it for details. 

For this frame I'm not seeing a way out of vertically supporting both the inner and outer rims though.

I do 2 flashings, the lower flash goes behind the ledger and kicks out under it, this would also protect any wall finishes below. The counterflash shingles over the 1st flashing and kicks out over the ledger. The housewrap or foam is shingled over the counterflash. imagine pouring water down the wall from above, everything should be lapped to kick the water out of the wall, "think like a raindrop".

[Erin]

For this frame I'm not seeing a way out of vertically supporting both the inner and outer rims though.

Yeah, that's the direction I've been leaning. 
I mean, when I was originally planning, it was just a ledger, attached the house.  But once I've started looking at the actual logistics of that, I just couldn't see how I was going to be able to do so...

But, if I go with an independent frame to support the actual weight of the deck, I can do pretty much whatever I need at the ledger to make it shed water as it's for lateral stability rather than load support.

[UpToNoGood]

I attached my pergola to my house like a deck a few years ago.   I did a lot of research and didn't want lag bolts going in to my house where water could follow them in and cause damage.  This is what I came up with.

http://www.deckbracket.com/

[Adam Roby]

Isn't that the same website that MushCreek posted above?   

I like the look of these, but they ain't cheap:

http://www.deckbracket.com/

[UpToNoGood]

Isn't that the same website that MushCreek posted above?   

Sorry I missed that, but I have used them and they work great.