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tschmidt
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Milford, NH
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Greenhouse mold problem

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Greenhouse
We have a lean-to greenhouse built from pressure treated lumber and glazed with polycarbonate panels. I tightened it up a little this summer and for the first time we have a problem with mold on the rafters. I though mold would not like the chemicals in PT lumber but that does not appear to be the case.

Just to be clear this is inside, the staining on the siding I assume is a reaction with the aluminum flashing and rain splash back.

During nice weather been opening it up to dry things out and we will need to be more careful watering the plants.

Once we get humidity under control what is the best way to remove mold? I plan to wipe the lumber down with bleach. Is that the best solution and is there anything I can treat the lumber with to inhibit mold?

/Tom


cowboyro
Premium
join:2000-10-11
Shelton, CT
said by tschmidt:

I tightened it up a little this summer and for the first time we have a problem with mold on the rafters.

There's your problem. Too much humidity and lack of air circulation. There are chemicals you can spray and they will kill the mold - look at power washer additives.


Jack_in_VA
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join:2007-11-26
North, VA
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reply to tschmidt
Is that T1-11 siding on the house?


DataDoc
My avatar looks like me, if I was 2D.
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join:2000-05-14
Martinsburg, WV
reply to tschmidt
You may also be causing a problem in the area of your house wall that is covered by the greenhouse.


tschmidt
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Milford, NH
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reply to Jack_in_VA
said by Jack_in_VA:

Is that T1-11 siding on the house?

Nope - 1x8 V match.

The house is timber framed with stress skin walls and roof panels.

/tom

kherr
Premium
join:2000-09-04
Collinsville, IL
I had a house like that years ago. Almost 2000 sq.ft. All electric with a small wood stove in the middle of the house, had $35 electric bills in th winter ........


tschmidt
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said by kherr:

I had a house like that years ago. Almost 2000 sq.ft.

Interesting you mentioning that. That is about the same square footage as ours, two story cape with a walk out basement. Used a local timber framer to design and erect the frame and panels then did most of the rest of the work ourselves.

We heat with wood. The stove is in the basement, which is why a walkout basement was so important. Many years ago I added a heat exchanger to the wood stove to act as a preheater for hot water.

We use about 2.5 cords of mixed hardwood a year for space heating and it provides about half our hot water during the winter. When we built the house installed electric baseboards but have only used them a few time during long trips when no one is home. Electricity in NH is pretty expensive.

We have a lot of land so I'm able to harvest cord wood from our own property. Very comforting seeing a couple of years worth of wood stacked up, knowing no matter what else happens at least we will be warm.

/tom


tschmidt
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reply to DataDoc
said by DataDoc:

You may also be causing a problem in the area of your house wall that is covered by the greenhouse.

That is a possibility but the temperature differential is small and the wall is warm relative to the greenhouse. So at least water is not condensing on or in the wall. Also most, but not all of the north greenhouse wall uses stressed skin panels that are impervious to moisture.

Regardless, I agree we need to do a better job controlling humidity.

/tom


norton

join:2005-08-03
Howard City, MI

1 recommendation

we live in deep woods and use either bleach or vinegar to control moss/mold on brick.

averagedude

join:2002-01-30
San Diego, CA
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reply to cowboyro
said by cowboyro:

said by tschmidt:

I tightened it up a little this summer and for the first time we have a problem with mold on the rafters.

There's your problem. Too much humidity and lack of air circulation. There are chemicals you can spray and they will kill the mold - look at power washer additives.

Do some google'ing and you will find out that greenhouses need ventilation to control humidity. Obviously you don't want to over ventilate, then you might as well be outside. But under ventilation will cause the moisture (relative humidity) to rise with the higher temperature (warmer air holds more moisture) and thus allowing the moisture to condense out at relatively warmer temperatures on the structure.
I have seen very simple set ups where a line voltage humidistat is connected to a simple bathroom (fart fan) to control condensation.
Or, you could just put back the holes you fixed (vents) in the structure and let it breathe naturally. A small vent low and high on a will should do the trick.


hortnut
Huh?

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reply to tschmidt
said by tschmidt:

I tightened it up a little this summer and for the first time we have a problem with mold on the rafters. I though mold would not like the chemicals in PT lumber but that does not appear to be the case.

Once we get humidity under control what is the best way to remove mold? I plan to wipe the lumber down with bleach. Is that the best solution and is there anything I can treat the lumber with to inhibit mold?

/Tom

Need a small fan, a cheap $20.00 box fan would work, as a way to ventilate during periods of high warmth/humidity.

One can get very fancy and hook a fan up with a humistadt and thermostat to control fan and vents.

One can get commercial products to get rid of surface mold, but plain old bleach cut with water works. Just use gloves in application and do not get it on any desirable plants.

In my 30 x 96 Propagation House, had the cheap box fans hung around various points of the House that ran 24 hours/day. And then vents that opened when temperature reached a certain point, with a fan that started at time of vent opening.

Used something similar in the overwintering houses.


tschmidt
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said by hortnut:

Need a small fan, a cheap $20.00 box fan would work, as a way to ventilate during periods of high warmth/humidity.

Yea agree - we keep a box fan going to keep air circulating internally.

During the summer I built a controller to assist with natural ventilation. The windows are controlled by hydraulic openers that respond to temperature. We found that during the summer just opening the windows did not not move enough air to moderate temperature. So I use that as a justification to play. My wife is the one that uses the greenhouse, my interest is carpentry and electronics.

The controller does several things:

1) Fan in roof windows come on when internal temp hits hi set point.

2) The floor is pea stone so set up a blower to move air through the stone to help moderate winter temp. The controller monitors outside air. When temp falls below 38F turns the blower on. During the day this moves warn air through the stone and then at night extracts the stored heat. The pea stone is in addition to 6 55-gal barrels along the north wall. Using more drums would have taking up too much valuable space as the greenhouse is only 8x16.

3) If internal temperature drops dangerously low there is another fan that blows in basement air. The wood stove is in the basement so that is a cheap source of makeup heat.

4) If that does not bring up temperate enough the system sends a freeze warning email.

I've written up the controller on my site if you are interested:
»www.tschmidt.com/writings/Greenh···tion.pdf

The greenhouse controller is much more sophisticated then the system I designed for the wood stove decades ago. I'm trying to convince myself I need to upgrade it. But in truth I'm hard pressed to come up with additional features to justify the change. The thermocouple displays are no longer available so if they ever fail it will force my hand.
»www.tschmidt.com/writings/Wood_H···ller.pdf

/tom

TheMG
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4 edits
reply to kherr
said by tschmidt:

said by hortnut:

Need a small fan, a cheap $20.00 box fan would work, as a way to ventilate during periods of high warmth/humidity.

Yea agree - we keep a box fan going to keep air circulating internally.

Circulating the air internally will do absolutely nothing to control humidity. You need to ventilate to the outside to bring the humidity down. The humidity has to go somewhere, blowing air around in circles does nothing.

It really doesn't take much to keep humidity under control. A simple bathroom exhaust fan connected to a humidistat would be more than sufficient. Hell, the bathroom fan might even be too much. A computer type fan might actually suffice.

Something like this:

12V power brick --> humidistat --> computer fan (blowing air outside)

said by kherr:

I had a house like that years ago. Almost 2000 sq.ft. All electric with a small wood stove in the middle of the house, had $35 electric bills in th winter ........

How many years ago exactly?

Right now, if I used ZERO electricity, it would still cost me more than $35 of delivery charges, administrative fees, access fees, etc.


hortnut
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said by TheMG:

said by tschmidt:

said by hortnut:

Need a small fan, a cheap $20.00 box fan would work, as a way to ventilate during periods of high warmth/humidity.

Yea agree - we keep a box fan going to keep air circulating internally.

Circulating the air internally will do absolutely nothing to control humidity. You need to ventilate to the outside to bring the humidity down. The humidity has to go somewhere, blowing air around in circles does nothing.

It really doesn't take much to keep humidity under control. A simple bathroom exhaust fan connected to a humidistat would be more than sufficient. Hell, the bathroom fan might even be too much. A computer type fan might actually suffice.

Something like this:

12V power brick --> humidistat --> computer fan (blowing air outside)

said by kherr:

I had a house like that years ago. Almost 2000 sq.ft. All electric with a small wood stove in the middle of the house, had $35 electric bills in th winter ........

How many years ago exactly?

Right now, if I used ZERO electricity, it would still cost me more than $35 of delivery charges, administrative fees, access fees, etc.

.

I guess I do not know what I am talking about.

I was in the Business for over 30 years in the PNW, an area notorious for its high humidity in the fall/winter/spring. I have built and owned 2 separate Nurseries at two different locations and totally revamped one in another state.

My last Nursery, I had over 30,000 sq ft of Greenhouses, some heated and some not. And all needed some management to control humidity [and at times excess warmth/heat] and the Diseases it could bring. Mold on wood and such was the least of my worries. Disease was.

Some 30 inch fans were pushing over 10,000 cu ft per min through a series of tubes down the length of the Greenhouses.

I also managed IGC's that prior managers could not get a handle on their Greenhouses. Movement of air and control of heat were major contributors to their failures.

TheMG
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said by hortnut:

I guess I do not know what I am talking about.

When did I ever say that?

The reply wasn't even in response to your post.

tschmidt mentioned he already has a box fan circulating air inside the greenhouse, which apparently isn't solving his problem, so I suggested venting some air to outside.

Please stop taking things personally. This is a public forum where everyone is welcome to post their ideas and opinions. Nothing here says "if you're not an expert on the topic, please don't post". I admit, occasionally some of my ideas are not necessarily good ones. No one is intending that you don't know what you're talking about, so please don't take offense so easily.


hortnut
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1 edit
said by TheMG:

Please stop taking things personally. This is a public forum where everyone is welcome to post their ideas and opinions. Nothing here says "if you're not an expert on the topic, please don't post". I admit, occasionally some of my ideas are not necessarily good ones. No one is intending that you don't know what you're talking about, so please don't take offense so easily.

...snip..
said by TheMG:

Circulating the air internally will do absolutely nothing to control humidity. You need to ventilate to the outside to bring the humidity down. The humidity has to go somewhere, blowing air around in circles does nothing.

It really doesn't take much to keep humidity under control. A simple bathroom exhaust fan connected to a humidistat would be more than sufficient. Hell, the bathroom fan might even be too much. A computer type fan might actually suffice.

Something like this:

12V power brick --> humidistat --> computer fan (blowing air outside)

.

I am not taking things personally. My skin is pretty damn thick. Just trying to solve the OP's issues/s and offering solutions. Dude, we are actually on the same page.

Was trying to point out how important air movement is, in any size Greenhouse. And I too mentioned venting. In my opinion, both go together, both need to be properly sized and timed as to when to open vents, run fans, etc. And depending upon what the Greenhouse is being used for, that too is an art, in my opinion.

I am no where near an expert. I just practiced the art of growing things that provided my sole income for many years. And I made my share of mistakes.

I hope my posts have helped the OP and other posters.


dogwatch

@100.43.101.x
Others have addressed the moisture issue so I won't comment on that, but you really should install gutters and downspouts.


hortnut
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reply to tschmidt
Sounds like you have a lot of the basics covered. In my opinion, you just need to make some minor tweaks. This would be for your climate area, the orientation of the greenhouse and such.

Over the years have helped out a number in your situation and it is usually some minor adjustments that are needed.

You already have the basics in place. For me that is a fun item of a greenhouse, to make the adjustments.

The only thing different was that I had Frost/Temp. Alarms that activated a piezo alarm from Radio Shack near my bed once a set temp. was reached. Used a step down transformer hooked to a 24v alarm. Those got me up real quick!


tschmidt
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said by hortnut:

you just need to make some minor tweaks.

I've been thinking about how to install a small exhaust fan to control humidity. The controller has a humidity sensor in addition to temperature so the control function is easy. Looks like I have another project for next summer. Since the greenhouse is so small we don't need to move a lot of air. I'll try a DC muffin fan and high quality dryer vent (to minimize back draft) and see how it works.

said by hortnut:

The only thing different was that I had Frost/Temp. Alarms that activated a piezo alarm from Radio Shack near my bed once a set temp. was reached.

I use a Sonalert with the wood stove system. I make provisions for an audible greenhouse alarm if needed but I'm hoping that will not be needed. The biggest risk of freezing is during power outages so in that case the alarm is a moot point.

Thanks for your suggestions. I agree to fun part is tweaking the system. Hopefully the design was flexible enough to accommodate surprises.

/tom


tschmidt
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reply to dogwatch
said by dogwatch :

but you really should install gutters and downspouts.

In this part of the country gutters are relatively rare. Between leaves and ice dams they cause more problems then they solve.

/tom


tschmidt
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reply to tschmidt
Want to thank everyone for their suggestions.

I added a small exhaust fan on the east greenhouse wall to control humidity. Used a muffin fan I had in my junk box and a high quality metal dryer vent to prevent cold back drafts. The controller already had a humidity input so the software modification was a piece of cake.

We'll see how it works.

Come next summer when we empty it out will have to scrub down the inside.

/tom