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3-season room has condensation problem

wagnerm's picture

A friend (not me, really!) went around their builder and insulated (fiberglass bats in stud cavities and roof joists) their 3-season porch before the sheetrock was installed. They also paid the heating sub to run ducts (supply only) into the room. The room is closed off from the house except for evenings and weekends. Predictably, they have a terrible condensation problem now that winter has arrived but here's the question: The builder built the porch (uninsulated floor) over a crawl-space that is open to the basement. Isn't that a big problem even without the forced-air and insulation?

(post #59844, reply #1 of 22)

I don't understand why you'd think that any one of those three would be a problem. Obviously you can see the conditions better than I can.


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(post #59844, reply #2 of 22)

On the off chance that you have something to offer here I will restate the question. I don't think that the insulation has much to do with it either way and they can easily turn off or disconnect the ducts but I would like to know if the builder might be responsible for the part of the problem that can't be so easily fixed. I can look at this from a theoretical perspective but I am looking for a practical opinion to help my friend decide a course of action.

(post #59844, reply #3 of 22)

Where is the condenstaion showing up?

What is the construction of the room?

What is the condition of the this crawlspace? does it have a vaport varrier over it?

How cold is it?

Without knowing anyhting else about this my guess is that the problem is the heating ducts. They are forcing warm moist air into the room. There is no return air so the pressure builds up and the moist air is being forced out through cracks and getting cold in those cracks and condensing.

. William the Geezer, the sequel to Billy the Kid - Shoe

(post #59844, reply #4 of 22)

check your email mike. 

Remodeling Contractor just outside the Glass City.

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(post #59844, reply #7 of 22)

I don't take offense. Maybe I could have added my final thought to my preceding statement that you can see it better than I. It was implied but not stated that perhaps you could share some more details with us.

Insulation always halps decrease the amt of condensation so that can't be a problem. ( large amts of glass can be)

Heat helps prevent condensation, as a general rule, but running the temp in that room up and down and up and down will probably cause some extra condensation making it more a use problem than a design or construction problem.

I can't see diddly from here about the basement details. I won't even waste my time commenting there because there are a hundred different scenarios I can imagine. You need to describe what and how. Maybe I or somebody can help but we can't see what you presume we can.

But as noted by others, the use of the room has been modified beyond it's designed intent so problems can and should be anticipated in performance. The load is bearing on the owner who made those changes, not on the contractor.

A house is a system. It all works together. Change any one thing and multiple other items and systems within it begin to work differently. I have a saying that you can't change anything without changing everything. I explain to my customers that my designs are a tapestry, woven together carefully. Pick and pull at strands and the whole thing can unravel. Sounds to me like your friend is trying to use a half ton puckup truck to haul tons of gravel and hoping against hope that it will still look the same way it did when he drove it off the showroom floor..

Excellence is its own reward!

Edited 1/27/2004 10:35:20 PM ET by piffin



Oh Well,

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(post #59844, reply #8 of 22)

Thanks to all. Sorry, I didn't mean to 'dis' anybody but the first response seemed sarcastic and non-responsive. 

I am an active and aggressive DIYer but I always draw a line between my work and that of a professional that I have engaged to do a job. I would have strongly advised my associate against making any of the changes that they made. On the other hand, I'm told that they were encouraged (wink, wink) to do these things by their salesperson.

I just want to help get them pointed in the right direction to get this resolved starting with structural problems if there might be any.

(post #59844, reply #10 of 22)

I winced again and again as my associate related their problem and what they had done. I don't pretend to know much but it sounded like a disaster to me. I expressed no sympathy whatsoever until she told me about the open crawlspace. I had never heard of a 3-season room with a basement.

As I said in the reply to all, I just want to help get her pointed straight to get this new house right.

Thanks again.

(post #59844, reply #15 of 22)

again Mike, I am sorry to have been too brief in my first reply. Didn't realize you were less familiar with my 'shorthand'. Wait'll you get a load of some of my spelling from typing without proofreading.


anyways, I can't see any connection between the crawl situation and the condensation problem. Here in Maine I see hundreds of variations of similar connections with little or no problem. She could lay plastic on the ground in the crawl to keep groujnd moisture down. That wouldn't hurt anything, wouldn't cost much either, but probably wouldn't solve the problem. I think Mike plretty well explained things.

If she is going to use this as heated space, she should staple up fibreglas insulation under the floor and keep it heated all the time with the addition of a cold air return.

Or just wait for motre pleasent weather to use it. The problem with that scenario is that it will become a storage/junk room if she is like most folks.

Good luck and welcome to BT


Excellence is its own reward!



Oh Well,

We did the best we could...

(post #59844, reply #5 of 22)


like piffin said, you can see it better then us, so it is hard to say if something else is going on ( hey piffin , on another post someone said "where is piffin")

however I build  QUALITY sunrooms as part of our gig,

a lot of peolpe build two and three season rooms  and try to use them year round and have the same problems you do (oops your friend)

what causes condensation

tons of plants, hot tub, swim spa, year round use or lots of cooking (like pastas, steam veggies etc)

single pane glass, thin double pane glass, tons of glass

 ( there is a balance of where the inslation in the house  breaks even and the heat loss blows out the windows, remember heat rises and it can only rise and fill so much, before it moves down and finds and escape, an example , we built a house with a lot of glass, the energy aduit came back and said it was a waste of money to inslate  the roof past R-29 beccause the rest would blow through the windows, by code we had to insulate to r-38)

a damp crawl space due to a high water table or poor foundation drains

introduction of a lot of heat to a cold area ( they only use it at night) hey its been cold for hours , lets walk in and crank up the heat

is the roof cavity vented, is there a way for any kind of built up condensation to get out, weepage holes in the glass framing  or the partitions between the glass ,etc

remember, glass is often the weekest link in energy conversation in a relatively modern  house, the item with the lowest R-factor

so if you are trying to pump a lot of heat into an area with any of these conditins with a lot of glass, guess what happens,.............condensation

so the trick is to manage the condensation

if I or the builder knew how it was really going to be used,(all year instead of two seasons) then they could have set up and used better insulated glass and set up for drainage of condensation and venting

 I no longer build two or three season rooms, I know the average owner is going to try to use them all year, so why not be honest and go for it


lastly I dont like the comment that the owner went behind the builders/designers back

if  so

any problems

hey thats your/their fault

although we all know the builder will spend time trying to figure out the owners "cost saving" shortcut


(post #59844, reply #9 of 22)

Thanks for your response. I have nothing but respect for the contributors and I need to watch my mouth.

It has been my practice to post a short question to get a discussion started without providing a lot of (potentially) useless information up front.

Thanks again.


(post #59844, reply #6 of 22)

First Point - technical stuff

>>The builder built the porch (uninsulated floor) over a crawl-space that is open to the basement. Isn't that a big problem even without the forced-air and insulation?

Without other facts, no, I don't see that as a problem, although "open to the basement" sounds like there might be an energy issue. Is there an access cover between the basement and the crawl?

Condensation occurs when air is sufficiently cooled (typically by contact with a could surface) so that the water vapor condenses because cold air can't hold as much moisture as warm air.

As noted by others, that relatively moist air could be from the heating system (do they use a humidifier?) or from their use of the room.

I'm curious as to why you are saying the condensation is predictable, and then asking about the floor and crawl detailing.

As you describe it, the home owner introduced changes into the design and construction without the contractor's input. And it looks like maybe you're trying to pin the condensation problem on the contractor.

It seems to me that once the home owner started screwing around with the room, the contractor is off the hook.

Second point - Your Attitude

You know that fellow Piffen that you dissed? He is one of the most knowledgeable and respected people here. And there are a number of pro's here with an incredible range of knowledge and experience.

Personally, I take offense when you come and ask a question, giving insufficient information to fully diagnose the problem, and then show some attitude when asked for additional information.

Especially when you're trying to get something on a contractor by going to a contractor's forum!

The more I think about it, the more amazed I am!



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Edited 1/27/2004 10:07:30 PM ET by Bob Walker

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(post #59844, reply #11 of 22)

It would seem that the HO, by closing the room up most of the time and not having cold air returns, has turned it into a 3 season terrarium. As Bill Hartman said, I would be concerned with a vapor barrier in the crawl, but other than that the crawl wouldn't inherently be an issue. (many homes have partial basements or are completely built on a crawl)??

Remodeling Contractor just on the other side of the Glass City

(post #59844, reply #12 of 22)

but... is it acceptable to have unheated space over an uninsulated floor over a crawl? That just doesn't seem right to me.

(post #59844, reply #13 of 22)

mike... i'm a little bit lost here. an unheated space over ... an open floor over  a crawsl space.. as opposed to WHAT?

are you saying it sould be a slab ?

the unheated floor has nothing to do with the type  of foundation.. the foundation is what it is..

now.. here is one of the basic problems.. heated air carries more moisture vapor than cool air.. so... every time you introduce heated air into the 3-season room FROM the heating system of the conditioned part of the house  you are bringing in say... 80deg air at a RH of say 40% .. then they turn off the heat.. and the air cools and ALL of the vapor gets wrung out and deposited on every condensing surface in the room... usually the windows..

i build 3 -season rooms on some of our additons.. but they are always independent of the rest of the house..

maybe a wood stove .. point being .. the cool air IN THE ROOM gets heated it is already at a low RH.. say 10%..or 20%.. because it was cold air.. when it cools down it will still be whatever it was when you started..

they've got a hybrid beast that wasn't designed or spec'd to do what they are trying to do..

 they could make it work... insulate the floor... and insulate the windows.. insulate the attic... insulate the walls... and integrate the heating system

Mike Smith   Rhode Island : Design / Build / Repair / Restore

Mike Smith   Rhode Island : Design / Build / Repair / Restore

(post #59844, reply #14 of 22)'s a 3-season room additon we incorporated into this major remodel..

insulated vinyl windows ... insulated walls..... 20" of cellulose in the attic..even insulated plywood box headers....

tile floor...

wood stove heat.. ( and south facing glass... warm as toast on ANY sunny day)..

 but not one inch of insulation in the floor... if they want ...we can go back and retrofit the floor insulation.. but it was purposely left out.. it was NOT part of the contract...

and the rest of the house is heated by oil-fired hot water baseboard....

Mike Smith   Rhode Island : Design / Build / Repair / Restore

Mike Smith   Rhode Island : Design / Build / Repair / Restore

ltl_sesnow.jpg84.15 KB

(post #59844, reply #16 of 22)

"insulated vinyl windows ... insulated walls..... 20" of cellulose in the attic..even insulated plywood box headers...."

What would be the difference between that a 4 season room? Just the lack of full time heating system.

. William the Geezer, the sequel to Billy the Kid - Shoe

(post #59844, reply #17 of 22)

that and the uninsulated floor.....

half of it was an old deck... we extended the deck framing ..

 so we saved money by not putting a foundation under it.. and not having to oversize the boiler..

in our climate.. coastal Rhode Island.. this is really a 3 -season room... so , it's pretty cost-effective

Mike Smith   Rhode Island : Design / Build / Repair / Restore

Mike Smith   Rhode Island : Design / Build / Repair / Restore

(post #59844, reply #18 of 22)

I know, I started out talking about condensation in the room but I know that that is mainly due to the mis-engineered hvac. I don't want to belabor this but you have helped me clarify my ultimate concern.

My reference to an unheated space over an uninsulated floor over a warm crawl space goes to the builder's 3-season intent for this room. If you assume that this room is closed off and unheated during the winter then the tile floor is below 20 degrees for weeks at a time. I don't know what the r-value of 3/4" plywood is but it isn't much. It seems to me like this would be a 200 sq.ft. radiator on the outside and a dripping mess on the inside. They have already noticed the insulation on the inside of the crawl space walls is wet.

Thanks again for all the great discussion. I have printed the entire thread for further detailed review in the reading room so if this last question has been answered there is no need to respond, I'll find it.

Thanks again for all the great discussion.

(post #59844, reply #19 of 22)

This ALL seems to stem from one point.  The HO, by just changing one seemingly little item, has changed the whole environment. 

The contractor designed the room to be 3 season. ( basically a glorified exterior porch to be used 3 seasons when weather allowed)  If the envelope of the house is intact, up to the point of the room the it would not matter what the temp of the room, crawl, or any thing else was.( it could almost be considered a seperate building) It will just sit outside the envelope and freeze. It should not matter at this point whether it was buitl on a slab, crawl, full basement, stilts, or the bed of a pick up.

The HO decided to insulate.(no big deal as long as they didn't do any VB) (now it's a INSULATED frozen space adjacent to the house)

Now comes the problem. They decided to introduce heat to the scenario. They have now created a conditioned space which requires certain minimal requirements. One of these requirements being ventilation and change of air, which they have none. so they keep introducing warm, moist air to a cold, sealed enclosure.

You have not let us know whether or not a good VB was installed on the bottom of the crawl. This would be an issue if not.

Don't forget that the heat run going through the crawl, even though it doesn't terminate in the crawl, still has thermal loss and therefore is introducing warm air to an unheated, unconditioned space.

Edited 1/29/2004 9:29:09 AM ET by JHOLE

Edited 1/29/2004 9:29:47 AM ET by JHOLE

Remodeling Contractor just on the other side of the Glass City

(post #59844, reply #20 of 22)

Sorry, I am not making myself clear. The heat is turned off by now. The HO understands that they can't pump warm moist air into a closed off room and not have problems. It is back to being an out-of-season 3-season room, but it is 11 degrees in that room now and there is nothing between their basement and 11 degrees but 200 sq.ft. of plywood and ceramic tile. No insulation, no vapor barrier. The foundation walls are insulated but what does that matter if the floor is not?



(post #59844, reply #21 of 22)

We're gettin' there. Is there an access to the crawl, does it have a cover, is the basement finished, is the crawl completely open to the basement? (i'm looking as hard as I can but it still looks like a computer monitor from where I'm sitting)

There should be a vapor barrier on the FLOOR of the crawl. (fact)

There should be insulation on the outside wall of the crawl. (fact)


Remodeling Contractor just on the other side of the Glass City

(post #59844, reply #22 of 22)

now that the details are coming out, I think I see what you are worried about.

Warm moist air form the basement is condensing on the floor framing of the addition.

So just hang a plastic sheet ( or even use duct tape to seal it up) over the access openning.


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Oh Well,

We did the best we could...