How To Waterproof Exterior Deck Floor Joists Where It Connects To A Building - Flashing Ideas

[@ineedhoez]

This is so helpful. I have a mess and I need to understand what will fix the issue, so I can make sure that the repair proposal I recieve makes sense.

[@Anonymous-zv9hk]

You're very knowledgeable and thanks for pointing out the places in this example that can be rotted out by water intrusion, if not sealed correctly, and the need to pay careful attention to protecting from water intrusion any exterior part of a structure that is exposed to weather and/or can rot or rust. In most places, if water intrusion occurs and rots out or weakens the structural strength of hidden parts of the structure, the cost of repair tends to be enormous and every contractor and subcontractor with any connection to the problem ends up being sued. Cheaper to do it right the first time, and to have a good construction lawyer on retainer who will read any contract before you sign it, and help you evaluate and maintain the insurance coverage you will need, and for how long you will need to pay premiums to keep it in effect, based on your jurisdiction's statute of limitations on defective workmanship, particularly in situations where the damage from hidden defects doesn't appear until many years later. Never hire employees or use subcontractors who can't read the language the product instructions are written in and/or who tend to not read the instructions, regardless of your instructions. Use your cellphone to make a video record of each stage of work done properly, and keep those records, including the name of the person who shot the video, n your permanent computer files on that project - proper video documentation can save you, if you're sued or involved in construction arbitration over the problem.

[@heavenisgreen4810]

Thanks so much! I’ve been searching for several years on a good solution to this problem. No other contractor has been able to advise me let alone in such detail. Thanks!

[@gregvancom]

You're welcome!

[@carlblumenthal7211]

I do this on a regular basis. I prefer to waterproof between the joists, as well as onto the the sides of the joist approximately an inch with flashing tape. If the plywood isn't notched down between the joists, I install a block there, flush with the exterior wall. I use flashing tape under the joists, that is 2"+ below the bottom of the joists and is notched around the joists as needed. Under the 2"+ of tape hanging below the joists, I tuck more Z bend flashing that caps the siding under the joists. After the first round of the flashing tape is installed, I add a 2nd block over the 1st one, which is caulked all around, to effectively double the amount of waterproofing you can do. I do not do the metal all around the joist. I do see the advantage of it on the exterior sides of the end joists though, as well as caulking. The flashing placed on top of the joists needs to be a Z bend, notched at least 1/2" into the top of the joists. It also needs to extend out past the additional blocking at least 1/2" so water will follow the metal and drip down outside that block. This flashing covers the entire deck. I also caulk under this flashing as well as into the notch in the joist. This Z bend flashing is also taped directly to the plywood on the exterior wall, as well as a strip of flashing tape on top of the metal that covers the joists to protect it from the decking tearing the metal. A custom pan is used for any doors. All caulking used is not water soluble and can be applied to wet surfaces. I have a few preferences, but stick with clear for the caulking I listed above. Cheap caulk is cheap. Spend the money and get good caulk, as unfortunately, you are depending on it more than I prefer. It is also a good idea to caulk the tops of any double joists at least 12" away from the exterior wall to minimized water entering that gap, Flashing tape can also be used, but will be seen in any decking gaps. Cantilevered joists are a terrible idea and should be avoided or redesigned whenever possible because of these flashing challenges.

[@dansamson7081]

Thanks for video Greg, this is an awesome detail that is usually overlooked and troublesome.

[@gregvancom]

You're welcome and as someone who's had to repair some of them, it's even more true.

[@Straight-Outta-Roanoke-AL]

I didn't think about this. Thanks!

[@marie-angelewis6542]

This is good! We are facing water ingress onto a balcony that is tiled over a waterproof membrane which has now failed. Scary big job but has to be redone and I'm looking how to minimise the labour/cost. What you have done is excellent!

[@gregvancom]

You can do it.

[@Clark-Mills]

Also run damp proof course over the doubled up joists either side to prevent water running in between the doubled joists and wicking back (and never drying).

[@gregvancom]

Maybe a solid beam would even be better.

[@khalidhashimeh]

Awesome video dude..keep on rolling more..

[@gregvancom]

Thanks! Will do!

[@joshsadler9417]

this video and thread has been very helpful thank you. I recently bought a house with a cantilevered deck knowing it might be problematic and indeed it is. It's PT and in good shape, well built and seemingly well flashed, although it may not be metal flashed as you have demonstrated but likley done the same way with heavy black deck tape or rubbery window tape. It has siding over it now in between the joists so i can't quite see what he did but it seems to keep an exceptional amount of water and snow out as we're in vermont and get 5 in of rain a month, often driving windy downpours. 99% of the time it is bone dry but we noticed a bit of water and discoloration in a few spots where the joists are sistered so i tore open the wall to have a proper look. It appears that the water is wicking in through the sistered joists in between them not on the outside of them in a few spots maybe a few teaspoons a year, but enough to be a concern. Tiny bit of mold but no rot. Also, the water comes out at the bottom of the sistered joists and not the top on the inside of the wall. I did a few tests with pressurized bleach water, working my way from the top of the door jamb which is metal flashed, check for water leaks, then under the flashing above the joists, into the top of the sistered joists and along the sides of them, checked for leaks again, still nothing. Then i went back and sprayed under the joists and up into the intersection from below, still nothing. I'm starting to think that the water is wicking between the joists maybe from above and below the sisters and at a certain combination of wind driven rain or rain and snow and dripping in slowly. It seems like deck tape over the sisters on top is a good idea but also i'm trying to figure out the best way to keep it wicking up from the bottom. The deck is 2" below the door threshold and the deck does slope slightly down and away from the house. It does take quite a hit from falling snow and ice off two roofs even though it's only about 4' off the house. We're thinking of putting a roof over it to manage the rain and snow load but it would be foolish to think it won't still be quite rainy and snowy. I thought about a galvanized flashing over the sistered joists sandwiched between a heavy deck tape to try and get a drip edge under the decking. Also thought of drilling a 1/4 hole from the bottom, maybe angled away from the house, but not through to the top so that water that did bet in between the joists had an exit. perhaps a parallel one behind it filled with silicone? I will probably pull a bit of the cedar siding off to get a better look at what he's done but it seems not broke and i am cautioned to 'fix it". Any tips or insights from anyone would be greatly appreciated, Thanks!

[@gregvancom]

Email me some pictures and you can get our email address at our website.

[@godbluffvdgg]

The metal is the savior...:)...You showed it perfectly...I was ready to jump on you when you were talking "caulk"...Clear silicone in those inside corners of the joist would be fine...Those cantilevers are learned through experience...I wish I had youtube in the 80's when I started in this business...:)...Great job though!

[@gregvancom]

Thanks and good point about KZbin.

[@michaellevrini667]

The presumption in your video is that pressure treated wood (PTW) is used for the rafters thus they would be located within the house as well as outside, the latter as deck joists. Then PTW boards would be installed on the joist, not a roofing material such as EPDM or TPO. Is this all correct? I have a cantilever balcony where the builder did not use PTW joists and installed the aforementioned EPDM. After 8 years I have all kinds of moisture problems and need to replace out or sister rotted joists. We thought about doing what you describe, but would involve too much work to get the 2/3s inside the house, so we are doing the previous method and hopefully with better waterproofing.

[@gregvancom]

Keep in mind that some of these decks aren't built with pressure-treated lumber or any type of waterproofing and some of them don't ever have any problems.

[@dougstewart3546]

Excellent video, Greg. Thanks for the information1

[@gregvancom]

Glad you enjoyed it

[@gamking7987]

is it ok if to live my deck, or porch levevel with the inside floor? I got a brother on a wheel chair and they do not like steps, I am thinking about building it level with a nice slope out, it will also be covered, but I am not sure what the inspector its going to say, and as always thanks for the videos.

[@jasonlommerse4328]

My situation is similar, but my home is brick. I've got a cantilevered ("Floating") deck off the master bedroom where the joists enter "pockets" (I've heard them referred to this way). The joists were caulked at the brick and the caulk is failing so I've got water dripping from the top of the inside of a window in the living room below the deck. Other than pulling up decking and recaulking, is there something more I should do while I'm at it? I have not found ANY info on how these "pockets" should be sealed or flashed.

[@gregvancom]

Email me some pictures and you can get our email address at our website.

[@victorramos589]

The metal you’re using is it flashing metal? Like the one to wrap around windows?

[@gregvancom]

Yes, but it all depends upon the window. If you purchased a new window, then follow the installation instructions provided from the manufacturer or company who made the window.

[@amrohwary4410]

Is it okay to notch the joists the way you did? Wouldn’t that impact the strength of your cantilever. I’ve also thought about waterproofing the entire joists such that the deck joists are technically interior joists as well. Do you think that’s feasible?

[@gregvancom]

It will depend on the length of the cantilever and size of joist. Like a 2x12 might work better than 2x10 if it will fit into your floor.

[@larryzdanis5377]

I have the same issue.. I've read that PTW can rot through aluminum or galvanized flashing, so I was going to use copper. A roll of 20'x12" copper at HD was very thin and still not cheap.. don't trust it. The previous flasher used vinyl/plastic. What type of metal flashing do you recommend with treated lumber?

[@gregvancom]

I would check with the lumber manufacture to verify.

[@gyulnaraashari4113]

What thickness of the metal do you use?

[@gregvancom]

I can't provide product information, but can suggest asking someone at your local building material supply stores to find what contractors in your area are using.

[@Crazst]

If the joist gets wet, is there any risk of moisture transfer through the wood itself and drying into the wall cavity?

[@gregvancom]

Moisture can transfer from wood to wood and if it gets into a wall cavity that is not water proofed on both sides, it can evaporate. You will be more concerned with a leak that produces regular amounts of moisture.

[@grod1194]

What kind of metal do you to seal with silocone

[@gregvancom]

It should tell you in the silicone instructions on the product container.

[@kevinhornbuckle]

Water needs to be kicked off the top of the deck joists for their entire length. Doubled up joists will warp as they dry and rain will get trapped between them even if you caulk the top of the joint during construction. You can use galv steel stud tracks wider than the joists. There are implications for deck board fastening if you do this.

[@gregvancom]

What do you mean when you suggest that water needs to be kicked off top of the deck joist for the entire length? And good point about the doubler, maybe a solid beam would work better.

[@kevinhornbuckle]

gregvancom If water comes onto the beam, it had to have a way off the beam. I was thinking of a partially caulked horizontal joint between a doubled 2X. If the caulk stops or fails, water will run between the 2Xs and compromise them.

[@mihalistravianopoulos4631]

I have seen this problem. I also have seen another issue where decks joist starts to rot on top where the decking boards fasten. people sister onto the the joist so the the decking board will have a level surface to fasten onto. This sistering just accelerates the rot on that joist. I use deck joist tape in these situations. Also Something I have seen is on the flashing between the house and deck, they add whats called a "kerf" to stop water from coming back toward the house.

[@marie-angelewis6542]

@@mihalistravianopoulos4631 that's what we have. Water ingress from failed waterproofing has rotted the beams. Are builders obliged to waterproof the beams? Ours certainly weren't and we are looking at sistering with new but it might be another disaster for the future.

[@howtodoitdude1662]

This is basically waterproofing the building not the joists, correct?

[@gregvancom]

Yes, Joist can be protected sometimes with a strip of waterproofing materials over the joist, but I'm not 100 percent convinced this will always work.

[@gidgetkent6430]

When we think of rain we need to think wind blowing water uphill

[@gregvancom]

Yes, good point.

[@kevinhornbuckle]

If you are doing this work for yourself, make your flashing out of copper. Learn to form and solder copper. Silicone sticks well to clean, dry copper.

[@gregvancom]

Thanks for the suggestions.

[@jamesgarvey2090]

Be careful with copper and treated lumber. Some treatments will erode the copper flashing.

[@kevinhornbuckle]

@@jamesgarvey2090 Ideed. Thanks for the warning.

[@vivianoppong-kyekyeku2109]

I just found out my deck is leaking water into my siding

[@ghshomeimprovements]

Think like water and you should be fine

[@theMemphisSnuggler]

It's going to leak anyway, just don't build a cantilever deck.