# Building a room under an open deck so it is water tight?



## Don2222 (Aug 15, 2015)

Hello

I have seen many rooms under open decks fail do to water leaks and be torn down after a while. It was not in the budget to build a second story room so a little shack under the deck for a workshop or to store wood pellets inside seamed to be a good solution.

*Has anyone seen or done this successfully?
*
In this day and age with all the modern building materials, it does seem possible?

So in this bold attempt, I went with a full foundation 48" deep and polished concrete floor.
The foundation is 3,000 lb mix concrete and the floor is steel reinforced 4,000 lb stone mix with synthetic fibers to prevent micro cracking during the curing process poured over a base of 3/4" stone with sandy soil as the sub base. The 3/4" stone base allows for good drainage to prevent frost heaves.

Since the roof span is 12' and 1" of width is required per foot af length we used 2x12s. Then shaved them on an angle for a little pitch to shed water.

Next we chose Advantech premium wafer board which is far better than the old OSB junk that first came on the market.
The ability to NOT absorb water, hold the fasterners and stay stiff is very remarkable!
See video
http://www.huberwood.com/advantech/video/sIpwFgcZdzU

Two crisscrossing layers of Grace Ice and Water shield were layed on top of the sloping advantech and 6 inches up the side of the house under the shingles.

Now the shaved runners are being screwed back to the top of the shaved 2x12s with still some pitch to secure the open deck boards.

The Deck will be built using Fiberon composite decking and Fiberon railings.

See pics below.


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## Dr.Faustus (Aug 15, 2015)

many years ago I rented a house like this and the room underneath the deck was a total disaster. the poor landlord had to have it ripped up and rebuilt at least 3 times while I was there, which wasn't long. I was not present at any of the rebuilds so I don't know why it was failing so miserably. Seems like you are covering all the bases...


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## Don2222 (Aug 16, 2015)

Dr.Faustus said:


> many years ago I rented a house like this and the room underneath the deck was a total disaster. the poor landlord had to have it ripped up and rebuilt at least 3 times while I was there, which wasn't long. I was not present at any of the rebuilds so I don't know why it was failing so miserably. Seems like you are covering all the bases...



Thanks for your comments Dr. Faustus


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## velvetfoot (Aug 16, 2015)

We screened in the deck and put a metal roof on top.  We don't have a room under there, but I store stuff there and it stays dry.  Plus, the deck is very pleasant in the summer as far as the bugs go.  It was one of the better things we did.


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## Don2222 (Aug 16, 2015)

velvetfoot said:


> We screened in the deck and put a metal roof on top.  We don't have a room under there, but I store stuff there and it stays dry.  Plus, the deck is very pleasant in the summer as far as the bugs go.  It was one of the better things we did.


That is a good way to go. I was thinking of a roof over the deck but the wife and I did not want to go that route.
*Also with just a screened in deck if it rains real hard. does some rain come through the screens and go through the deck to the room below?*


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## Warm_in_NH (Aug 16, 2015)

Not sure I entirely get the pics, but we've always used 60 mil epdm rubber roofing as the roof. (Glue down, not mechanically fastened) Then sleepers (usually 2 x 4 on the flat) laid on top of the epdm with additional strip of rubber roofing (or rubber flashing) under each sleeper to prevent them from wearing through.  Always worked well but each situation is unique.


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## Don2222 (Aug 16, 2015)

Warm_in_NH said:


> Not sure I entirely get the pics, but we've always used 60 mil epdm rubber roofing as the roof. (Glue down, not mechanically fastened) Then sleepers (usually 2 x 4 on the flat) laid on top of the epdm with additional strip of rubber roofing (or rubber flashing) under each sleeper to prevent them from wearing through.  Always worked well but each situation is unique.


Good info, where do you buy the rubber  roofing?


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## Warm_in_NH (Aug 16, 2015)

I usually get it out of Harveys but they only sell to contractors. Although some local building suppliers carry it, RP Williams up in Bristol has it and I'm sure some down by you do too, just gotta call around. 
I'm sure with the help of some Google searches and you tube you can find an install video and instructions if needed.


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## Don2222 (Aug 16, 2015)

Warm_in_NH said:


> I usually get it out of Harveys but they only sell to contractors. Although some local building suppliers carry it, RP Williams up in Bristol has it and I'm sure some down by you do too, just gotta call around.
> I'm sure with the help of some Google searches and you tube you can find an install video and instructions if needed.


Thanks
What do you use for the roof?
Plywood or?


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## velvetfoot (Aug 16, 2015)

Don2222 said:


> Also with just a screened in deck if it rains real hard. does some rain come through the screens and go through the deck to the room below?


Maybe a little.  I wouldn't call it a room though.  Probably not what you want then, but we love our screened in deck.


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## Warm_in_NH (Aug 19, 2015)

Don2222 said:


> Thanks
> What do you use for the roof?
> Plywood or?



Hmmmm. Typed a full reply,thought I posted it bit don't see it here 3 days later.

For raht purpose "I" would use plywood.  Usually you use something with some give to it,but in that application movement t will be your enemy. 

I know it'll adhere well to plywood  (Advantech). The glue is essentially rubber cement, apply to both parts, let it flash off, carefully lay the roofing down. It's a contact adhesive,  when it's done it's done. 

We usually lay it all out,roll 1/2 the sheet back onto of itself,  glue, flash off,gently roll it back to where it came from hopefully without air bubbles.


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## semipro (Aug 20, 2015)

Assuming I understand your plan: 
I'd suggest providing access for clean-out under the deck boards.  Detritus will makes its way between the boards and if enough collects it may create water backups and standing water.  If using a hidden fastening system for the deck boards then access could be a problem. 
I assume you're using treated 2x12s?  Water will collect between those and the water shield rotting untreated wood. 
How much sunlight will make its way to the ice and water shield?  Its only rated for 120 days UV exposure.  EPDM, which is typically used for this application, has a high UV exposure resistance. 
You should consider putting flexible flashing (e.g., leftover ice and water shield) on top of your joists before installing the deck boards.


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## Don2222 (Aug 20, 2015)

semipro said:


> Assuming I understand your plan:
> I'd suggest providing access for clean-out under the deck boards.  Detritus will makes its way between the boards and if enough collects it may create water backups and standing water.  If using a hidden fastening system for the deck boards then access could be a problem.
> I assume you're using treated 2x12s?  Water will collect between those and the water shield rotting untreated wood.
> How much sunlight will make its way to the ice and water shield?  Its only rated for 120 days UV exposure.  EPDM, which is typically used for this application, has a high UV exposure resistance.
> You should consider putting flexible flashing (e.g., leftover ice and water shield) on top of your joists before installing the deck boards.



Thanks for your good comments. 

Yes the 2x12s are pressure treated and the 2x12s were cut on and angle so the roof is sloping. Then after 2 layers of Grace I&W was layed over the Advantech interlocking roof sheets, the tops of the 2x12s were bolted back on top to support the open deck floor. The fiberon decking will be screwed down so there is access.

Not much sunlight will hit the grace since the deck boards will be on top, but I am still concerned about the inability to resist UV rays as you know.
I was thinking about putting in aluminum between the joists on top of the Grace, my friend has a huge bending brake so Detritus (Good word! LOL) could easily slide down or be coaxed with a hose.

Good idea about the grace over the joist tops! I like that. See new pic below. Thanks.


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## Don2222 (Aug 21, 2015)

Hello

Still had water coming in when it rained. Putting in 2 windows stop it!  See Pic Below

Now all it needs is a door! ! !

Click pic to Enlarge:


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## Don2222 (Aug 26, 2015)

Hello

Got some PolyGlass today to go on top of the Grace I&W to protect the grace before the deck boards go on.
Is that a good idea?

see pics


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## Don2222 (Aug 28, 2015)

Hello

Polyglass is on over the 2 layers of grace I&W ! ! ! The light color pebble top on the Polyglass will not be harmed by UV rays and will reflect the heat. The Polyglass is tough stuff to cut!

The Polyglass interlocks with a tab with the same special adhesive that Grace has. Grace goes up 14 inches against the house under the shingles.

Some builders do a floating deck, but this is not floating, the joists are bolted into the 2x12s below the roof so it is stronger than a floating deck! The 2x12s below are tied to a ledger bolted to the house!

See pics below. Click to Enlarge


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## mustash29 (Aug 29, 2015)

I have 34' of 2nd floor deck and contemplated using this stuff years ago.  The brackets go on the deck joists, then the panels slip into the brackets.

http://timbertech.com/products/finishing-touches/dryspace-drainage-system/


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## Don2222 (Aug 30, 2015)

I have a customer with that Vinyl system under his deck. It works pretty well but is starting to buckle in a few spots.

This deck is almost as good as ours! They do admit the contact adhesive for EDPM is no good! The EDPM does not reflect heat!
Interesting how they used Grace over the stringers. 
See article
http://www.aconcordcarpenter.com/roof-deck.html

This deck is almost as good as ours! They do admit the contact adhesive for EDPM is no good! The EDPM does not reflect heat!
Interesting how they used Grace over stringers. 
See
http://www.aconcordcarpenter.com/roof-deck.html
They installed ¾” CDX plywood over the joists with construction adhesive and coated decking screws.
*I like the AdvanTech much better!


Unmatched Moisture Resistance
Designed for a longer exposure during construction, backed by a 500-day weather resistance guarantee. So unlike OSB and plywood, AdvanTech® sheathing is engineered to resist swelling, cupping and delamination
*


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## Don2222 (Aug 31, 2015)

Hello

The 7 tubes of Premium Henrys with the lifetime guarantee or what is known as Black Jack flashing sealer went on today.

As a test, every drop of condensation from the air conditioner rolled down the roof and jumped off!

See pics


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## Hogwildz (Aug 31, 2015)

Black jack will crack and separate over freeze thaw periods. If you didn't run the Grace under the boards, it will leak in time.
The SBS sealed with black jack will not stay tight very long.
Not to mention, the wood will absorb moisture & water, which will find it's way under the roof cement.


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## Don2222 (Sep 1, 2015)

Hogwildz said:


> Black jack will crack and separate over freeze thaw periods. If you didn't run the Grace under the boards, it will leak in time.
> The SBS sealed with black jack will not stay tight very long.
> Not to mention, the wood will absorb moisture & water, which will find it's way under the roof cement.


There is 2 layers of Grace under the boards! This is premium Henry's that is better than Black Jack with a lifetime guarantee. The wood is also Pressure Treated. So what else could be done?


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## Hogwildz (Sep 2, 2015)

Don2222 said:


> There is 2 layers of Grace under the boards! This is premium Henry's that is better than Black Jack with a lifetime guarantee. The wood is also Pressure Treated. So what else could be done?


As long as the grace is its own layer under the boards, you should be good to go. "Black Jack" no matter what brand or warranty, is only good for temp repairs/small hole patching etc. It is basically roof cement in a caulking tube. Some claim they are special, elastometric, etc., but it is mainly roof cement, just like you can get in 1 gallon & 5 gallon cans, just merely in a convenient caulking tube size.
Over the period of a few seasons of expansion & contraction, it will crack and fail. Wood is wood, and will absorb water, which some will find its way under the SBS, but as long as the grace is underneath you should be good, the rest is just a protective cover for the grace.


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## Don2222 (Sep 2, 2015)

Hogwildz said:


> As long as the grace is its own layer under the boards, you should be good to go. "Black Jack" no matter what brand or warranty, is only good for temp repairs/small hole patching etc. It is basically roof cement in a caulking tube. Some claim they are special, elastometric, etc., but it is mainly roof cement, just like you can get in 1 gallon & 5 gallon cans, just merely in a convenient caulking tube size.
> Over the period of a few seasons of expansion & contraction, it will crack and fail. Wood is wood, and will absorb water, which some will find its way under the SBS, but as long as the grace is underneath you should be good, the rest is just a protective cover for the grace.


Thanks for your comments.
The Grace as you say makes it watertight. Since the Grace should not be left exposed, the polyglass and Henry's is just a cover to protect the Grace from the sun and UV rays.


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## begreen (Sep 2, 2015)

Sounds like Grace under fire.


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## Don2222 (Sep 3, 2015)

begreen said:


> Sounds like Grace under fire.


Yes but now the application is clear and all is good! 

Just preparing for some rainy or snowy cold days!


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## Hogwildz (Sep 3, 2015)

Since you are installing decking planks above the membrane below, I doubt the Grace would suffer exposure issues, but covering was a good decision.
The extra yard gone is always a plus.


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## Don2222 (Sep 3, 2015)

Hogwildz said:


> Since you are installing decking planks above the membrane below, I doubt the Grace would suffer exposure issues, but covering was a good decision.
> The extra yard gone is always a plus.


Thanks. I agree but the Grace had some wrinkles so there was some pooling of water. The Polyglass has a nice hard shell so the water runs right off!


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## Don2222 (Sep 3, 2015)

New room inspected OK prior to decking! Horay! That was the tough one ! ! !


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## Don2222 (Sep 12, 2015)

Time for the Fiberon!


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## Don2222 (Sep 19, 2015)

Still no leaks and almost done !
Click to enlarge:


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## Hogwildz (Sep 22, 2015)

Looks great, nice work!


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