Ext. trim - where does the flashing go?

[Tom Anderson]

I'm planning to install a 3/4 x 9-1/4" MiraTec "skirtboard" and top it off with a piece of PVC drip cap. Siding will be Hardi. Should I install some sort of flashing (like Z-flashing) under the drip cap or should I just caulk between the skirtboard and drip cap during installation? Same scenario over the windows, except the top piece will be 5/4 x 6" MiraTec.
I don't want to overkill it just for the sake of overkill and can't really see where flashing would do much, if any, good in this situation. Any thoughts.

[Lavrans]

Re: Ext. trim - where does the flashing go?

I'm planning to install a 3/4 x 9-1/4" MiraTec "skirtboard" and top it off with a piece of PVC drip cap. Siding will be Hardi. Should I install some sort of flashing (like Z-flashing) under the drip cap or should I just caulk between the skirtboard and drip cap during installation? Same scenario over the windows, except the top piece will be 5/4 x 6" MiraTec.
I don't want to overkill it just for the sake of overkill and can't really see where flashing would do much, if any, good in this situation. Any thoughts.

What sort of drip cap?

If you're doing what I would call a water table: a trim piece that's coming over the skirt at an angle with a drip-edge cut into the bottom, it shouldn't need the joint between the skirt & drip cap to be caulked, because water shouldn't be able to make it back up there. You can caulk it if you want...

Bigger question is how you're going to flash the drip cap. I've attached a picture of the one I make below- I have flashing made up that covers over the upper part & turns down a little. Covers the nail or screw holes.

[Tom Anderson]

Re: Ext. trim - where does the flashing go?

Lavrans,
Yes, I think the correct term may be "water table". The drip cap I'm talking about is the kind that you can purchase most anywhere - they are about 1-1/2" wide with a slope to them and a kerf cut underneath near the edge to cause the water to drip off.

I wasn't able to see a picture. ???

[Stuccoman]

Re: Ext. trim - where does the flashing go?

IRC

R613.5.1 Anchoring requirements. Window and glass
door assemblies shall be anchored in accordance with the
published manufacturer.s recommendations to achieve the
design pressure specified. Substitute anchoring systems
used for substrates not specified by the fenestration
manufacturer shall provide equal or greater anchoring per-
formance asdemonstrated by accepted engineering practice.

R703.1 General. Exterior walls shall provide the building
with a weather-resistant exterior wall envelope. The exterior
wall envelope shall include flashing as described in Section
R703.8. The exterior wall envelope shall be designed and
constructed in such a manner as to prevent the accumulation
of water within the wall assembly by providing a water-resis-
tive barrier behind the exterior veneer as required by Section
R703.2.

R703.2 Weather-resistant sheathing paper. Asphalt-satu-
rated felt free from holes and breaks,weighing not less than 14
pounds per 100 square feet (0.683 kg/m2) and complyingwith
ASTM D 226 or other approved weather-resistant material
shall be applied over studs or sheathing of all exterior walls as
required by Table R703.4. Such felt or material shall be ap-
plied horizontally, with the upper layer lapped over the lower
layer not less than 2 inches (51 mm). Where joints occur, felt
shall be lapped not less than 6 inches (152 mm).
Exception: Such felt or material is permitted to be omitted
in the following situations:
1. In detached accessory buildings.
2. Under panel siding with shiplap joints or battens.
3. Under exterior wall finish materials as permitted in
Table R703.4.
4. Under paperbacked stucco lath.

R703.8 Flashing.Approved corrosion-resistive flashing shall
be provided in the exterior wall envelope in such a manner as
to prevent entry of water into the wall cavity or penetration of
water to the building structural framing components. The
flashing shall extend to the surface of the exterior wall finish
and shall be installed to prevent water from reentering the ex-
terior wall envelope. Approved corrosion-resistant flashings
shall be installed at all of the following locations:
1. At top of all exterior window and door openings in such
a manner as to be leakproof, except that self-flashing
windows having a continuous lap of not less than11/8
inches (28 mm) over the sheathing material around the
perimeter of the opening, including corners, do not re-
quire additional flashing; jamb flashing may also be
omitted when specifically approved by the building of-
ficial.
2. At the intersection of chimneys or other masonry
constructionwith frameor stuccowalls,with projecting
lips on both sides under stucco copings.
3. Under and at the ends of masonry, wood or metal cop-
ings and sills.
4. Continuously above all projecting wood trim.
5. Where exterior porches, decks or stairs attach to a wall
or floor assembly of wood-frame construction.
6. At wall and roof intersections.
7. At built-in gutters.

[Tom Anderson]

Re: Ext. trim - where does the flashing go?

Bill,
That's nice and all, but I've never seen an inspector pay any attention to how trim is flashed. Unfortunately, it's the poor flashing and lack of attention to water intrusion that does the most damage - at least from what I've seen.
I have to remind myself that the Codes are written mainly to project someone from getting injured...they don't care if the house isn't level and plumb and leaks water 2 weeks after a cert. of occupancy is issued.

So, if I have a piece of wood trim that is covered by a piece of PVC drip cap, does #4 apply?

[Bill Robinson]

Re: Ext. trim - where does the flashing go?

It would be simpler to see the detail drawn.

However I would be inclined to put a piece of rigid flashing first over the skirt board, flashed to the wrb and then apply the drip edge and then the siding.

Over the window I would put the rigid flashing over the trim.

You are right, most code officials do not check if the flashing is correct, the evidence is everywhere that they do not.

Rigid flashing would be metal, or PVC bent in an "L" shape with a "drip".
Drip cap is a fuller profile made of PVC, wood or composite.
All of this should have a slight positive slope to the outside.

Bill R

[Lavrans]

Re: Ext. trim - where does the flashing go?

Lavrans,
Yes, I think the correct term may be "water table". The drip cap I'm talking about is the kind that you can purchase most anywhere - they are about 1-1/2" wide with a slope to them and a kerf cut underneath near the edge to cause the water to drip off.

I wasn't able to see a picture. ???

sorry, maybe it'll work this time.

[Tom Anderson]

Re: Ext. trim - where does the flashing go?

Lavrans,
Well, I see a link, but can't find any software that will open a file with a .skp extension. Can you provide a .jpg or .bmp file, please.

[S.Joisey]

Re: Ext. trim - where does the flashing go?

.skp is a file created by Google Sketch Up - a 3D drwing program. THe basic program is free (do a seach for "google sketch up). If you don't have it, get it. It has made a big difference for a lot of us - likely fo you also.

And .skp files can be converted to .jpg files. I do this when emailing drawings to my clients.

[Lavrans]

Re: Ext. trim - where does the flashing go?

Sorry, I can convert to .jpg, but I'll wait until you say you don't want to use Sketchup first. I thought everyone had it by now... living in a bubble I guess.

[Joe Carola]

Re: Ext. trim - where does the flashing go?

Sorry, I can convert to .jpg, but I'll wait until you say you don't want to use Sketchup first. I thought everyone had it by now... living in a bubble I guess.

Lavrans,

I saved it for you in 2d graphic so that you can see it.

[No faux zone]

Re: Ext. trim - where does the flashing go?

Holy over kill bat man!

We don't flash that much here in the snow belt and before you say it, some of these original skirt details still survive sometimes 150 yrs or more.

As far as I've ever known, you should never caulk under cap flashing. Provided that the drip is far enough ahead of the trim and has the proper angle for watershead. You should only need to flash from behind the botttom coarse of siding and onto the cap or sill above the skirt. That is were the water needs to be diverted. The flashing under the cap is overdoing it in my opion. The drip rip under the cap in the previous drawing should take care of any back travel from the heavy rain loads.

[J.Buesking]

Re: Ext. trim - where does the flashing go?

I do it like Joe posted. The water table might break down in 10 years but your aluminum flashing will stay forever. It doesn't take much time or cost to run the flashing so why not.

[Lavrans]

Re: Ext. trim - where does the flashing go?

Holy over kill bat man!

We don't flash that much here in the snow belt and before you say it, some of these original skirt details still survive sometimes 150 yrs or more.

I do the flashing above the water table, not the one over the skirt- that one was put in as an illustration of what stuccoman quoted, although it's overkill.

I didn't put in the little z that I put in under the skirtboard if it's a bellyband & will have siding underneath (rather than if it's a skirt over the foundation- in which case the skirt should lap over the foundation).

Hey, Joe- do you have any idea why I couldn't upload the jpg to JLC? I tried saving it, even reduced the size, but the JLC page would just go blank when I tried uploading it.