My wife and I are just getting back into vegetable gardening, after having other diversions for the past 20 years - or so. I suppose the renewed interest is partly due to empty-nest syndrome, but we did sell our marina-kept big boat, so will have more time available for gardening during warm weather.

After doing a bit of research into some cold frame basics, I designed a unit to receive the sash from an old triple Pella wood casement I had removed from the house and replaced with a new unit several years ago. It's still in good shape and has insulating glass.

Following are a few photos taken yesterday of the partially completed unit - in position over a brick base in my back yard.

Aside from purchased 1x8 PT pine boards, galvanized hinges w/loose brass pins and foil faced rigid insulation, I re-used surplus materials I had on hand. For example, the brackets for the prop-bars were cut from some aluminum angle stock and secured with stainless steel bolts + nuts. The support pegs for the prop bars are simply sections of 1/2" copper pipe driven though holes drilled through the sash mullions

I sketched some quick details on an 8-1/2" x 11" sheet as a guide - but of course, ending up improving on things during construction.

With this much done now - I won't need to deal with building it in the Spring and can focus on getting indoor plants going in preparation for the transfer.

Part of my plan was to have the option of making this a Hot Bed, by installing a heating cable under the cold frame bed - which I understand must be set over 4" of sand. I've read that 1/2" wire mesh (hardware cloth) should then be placed over the cable, followed by 4" of soil, or planting mix. I'll most likely simply place seedling trays and pots directly over the bed - instead of growing directly in the soil.

I have not yet done much research into which heating cables may be best and how long of a cable is required for a 3'-4" x 6'-0" frame. Since this is new to me, I'm hoping to get some recommendations here from a few gardeners who have had success building hot beds, along with any helpful tips and advice.

I'd also like to hear any constructive criticism of this design, so I may make necessary changes before next season, how best to run a 40 foot long UG electrical cable from my garage service to the frame, what thermostats are good choices, the feasibility of automatic vents (12 lb lifting load) and anything else that I may be missing.

All best - Steve

That is the most beautiful cold frame I have ever seen. You did a great job. The brick base should provide a good heat sink, too. I have one question, however, and that is why you chose to place it in such an exposed situation where it gets no respite from sun/wind/temperature extremes.

I sometimes set up temporary cold frames but usually erected them against the south side of an existing structure, like my chicken coop. That way, when a really freaky cold snap hit, I could bale them over with foam sheets or hay more easily and they'd get some protection and ambient heat from the structure and have one less side where wind was a factor. Also, if you had power in that structure, a shorter distance to run electricals if you should so desire.

I suppose it is in an exposed location - but since the back of my house faces north, I wanted the cold frame to get full sun w/o getting shaded by the house - was this logic misguided?.

The frame is also alongside the rear row of our first-phase 20 x 28 veggie garden. When (or if) we expand the garden area, it will extend to the front of the cold frame. If I need to relocate the frame, the expanded garden can cover the excavated area . . . not difficult to move.

We have some raised planting beds as well, adjacent to the garage wing - where I suppose the frame can be moved to easily enough if that location would be best. I don't see the electrical cable distance as a problem, since I will need to install electrical conduit to the planned greenhouse anyway - which is currently planned to be sited near the cold frame, along the rear property line.

Another consideration I had was to re-install the Pella micro-blinds between the 2 panes of glass. They came with the windows and can be opened or closed with the remote turn-knob - enabling shading of the interior during warmer weather . . . just a thought of course.

Very impressive work.

My suggestions:

1. You may want to make the windows higer. They seem too low to me at the low point.

2. You may want to consider spring load or a counter balance the windows. This will make operating the windows much easier.

3. Electric heating the soil may be not practical. You are heating all the earth below.

4. Treated wood can warp if subjected to different moisture conditions on each side. Your foil-faced insulation is a very good detail as a moisture barrier. Still, you may want to paint both sides first.

5. I can't see nails or screws. How did you frame the whole thing?

dcarch

Great suggestions - most of which have been considered. I didn't want to make the frame too high but did desire a somewhat steep glazing angle. You're right - the front inside clearance is about 9-10". I could simply add brick courses to provide more interior height . . . have a ton of old bricks.

The sash aren't heavy - but I will consider counter balances, or interior springs attached to the prop bars to assist lifting. The prop bars are actually designed to be self-activating, which lock onto the peg stops by gravity.

You may be right about the heating cable - thought it might allow for even further extending the growing season.

I was allowing the PT wood to age a few months before staining - perhaps a Hunter green color; foil facing is just friction fit for now, so both sides can be finished for stability. I banded all exposed foam edges with 1 x 1 trim.

I ripped PT 2 x 4s into 1-1/2 x 1-1/2 stock and used that for internal corner posts. The horizontal boards are screwed to each post from the exterior with coated deck screws - as seen in this pic:

I used 3/4" x 2" PT trim strips to cover the boards end grain, using galv. finish nails for the trim. The perimeter 2 x 3 along the base, serves as a compression support.

Yes Autocad has advantages. Too expensive. TurboCAD will give you everything, less than a 10th of the cost.

Hand drawing is good, except you can't e. mail hand work. pdf files from CADD are great to scale up or down and send and print.

Regarding counter balancing: I actually knew your cleaver prop bar design intend. I was thinking more for your thermally operated mechanisms, the lighter the easier for them to operate.

Again, impressive work.

dcarch

But dc, you've heard of Epson and Acrobat, haven't you? ;-)

BTW - your work is also very impressive :^)

No your logic isn't misguided, you don't want a shady situation. I have outbuildings, and that made it easier for me to find an appropriate southern exposure with a building as a windbreak. The chicken coop just happens to abut my vegetable garden, so it was handy in all sorts of ways, including putting the poo close to the garden to compost in winter. LOL.

Some people earth mound around the back of their frames, but even a bale(s) of straw can serve as a good insulator if need be. There shall be spells when you might find it'll make all the difference if you get freakishly cold snaps after your plants are already up and growing. Are you planning on sowing directly in the soil or in trays/pots? Some sort of insulation will really help to retain the heat you trap in your frame through the nights. Even if it's bagged up leaves.

By early Spring - when I plan on simply placing trays/pots over the bed (not directly in the ground) I could stack bales of straw against the sides . . . it certainly won't hurt. If the forecast is for extended freezing conditions, I could always bring the trays into the garage until conditions improve.

Thanks for the comments - I truly appreciate them.

Dan

Dan

First, the front wall IME should always be as low as possible Why? The solar angle from Nov 15 - Feb 1 is too low for a high wall. You want sun to strike the soil to heat it, and a high front wall makes a long shadow. Short wall, plant maché. Don't re-do with a higher wall. That is fine and your angle for the glass is fine and if anything I'd make a little steeper to cut down the angle of incidence. My latest I was looking at tonight and looking at my scraps of polygal and thinking I could have done a two-layer window (% ~R-5) on the front wall for ~33-50% of the face to let in more light

Second, bricks are fine but you'll get, IME, better performance with something going farther down into the soil for insulation if you want to go all year. In that zone you don't need supplemental heat.

Third, I like how you lift the windows. Nice nod to history and improving upon it. When you do another, you'll want to think about an auto vent opener in there so no one has to go out twice a day. I'll post some pix to PhotoBucket soon to show what I did with my latest.

Fourth, a major modification for me in the wind was lips to stop the wind from hitting the joints/weatherstrip directly. I'll post a detail to elaborate. Even tho you have a clean joint, the wind likes to steal. Your wish for better and more salad throughout winter will reveal this issue.

Last, clean and well done. The sills allowing for rain to collect and not run off is a function of the discipline, IMHO, and I get to see Liebeskind's DAM leak all the time and the poor crews try to fix. 6º on the sills and you're good. Please think about how you can scale this up for folks in the area and how your community can make a few of these for those who need greens in the winter. San Diego is ahead of me in my scaling up but we all share and many among us can utilize such a box...

TTYS

Dan

dcarch

dc, I constructed a very simple heliodon a while back for a model of a passive solar house - simply a gyroscopic base and movable light source. It's definitely more intuitive than computer programs.

Re: thermal protection below grade, I intend to use some left-over rigid insul. to apply to the inside face of brick, 3 courses down or 8" deep - and overlapping the upper insul board where it'll be sealed with panel adhesive.

I'm ahead of you with the vent opener - ordered this unit last night:

It automatically opens at a user-set temp of 55º - 80º , I believe. The lift load is claimed to be 15 lbs, or a 30 lb sash weight. I think it should easily lift the center sash. Otherwise, a counterweight can be devised somehow.

I'd like to see your wind-seal detail, although I do have some neoprene bulb weather stripping left from another project. I plan on stapling that with Monel staples all around the top frame joints - protecting all 3 units (I'm a life-long boat owner with tons of boating gear and tools).

You've lost me somewhat on your last item referring to the sills not allowing for rain run-off. The entire top edge is sloped 22.5º - allowing for moisture to migrate around ea. sash. The 2 mid-mullions will have a neoprene gasket, providing a channel to funnel water to the lower front panel, where it will drip off the 1 x 2 trim.

Good idea about spreading the cold frame joy to the community - although, you'd be amazed at the level of organic growers on my island community . . . I consider my meager efforts falling somewhat behind that mainstream. Although, I'm catching up :-).

Thanks again for all your thoughtful time.

dcarch

One question though - how are you supplying DC power to the fan?

Yes, that's a brushless computer "muffin" fan, quiet and efficient with a 50,000 hour rated life.

I don't need to enclose the wiring because it's low valtage.

DC power is from a old computer 12V power supply.

Thermosat is a cheap($5.00) bi-metal room thermostat with one contact for cold and one for hot.

When it gets hot, the fan goes on, when it gets cold it kicks on a heater (with a relay).

dcarch

Regardless of the wires being low voltage, the very high humidity could short out the connections (didn't use marine grade connectors and some bare wires are showing ;-). Looks messy as well - I would at least bundle the wires in a plastic cable chase.

You noticed that everything is mounted using just Velcro tapes?

The whole thing is just a quick setup for about a month then removed. My greenhouse is removable and to be reinstall quickly every season.
Check this out:
http://www.youtube.com/watch?v=MzDqDBw_F54

dcarch

Seems as though you have a passion for metal arts and tomatoes . . . idle diversions from architecture?

I enjoy everything that has to do with beauty and science. Architecture is one of them.
Check out my posts in the " Cooking Forum" and the "Junk forum" here in GW.

dcarch

Basically, I wrote that I suggest the next incarnation has a steeper angle - mine is 30º - to have less reflected light and a better angle of incidence for the low winter sun. Last winter I didn't heat my coldframe in Denver area and had greens all winter. No electricity required.

Dan

In September, I will be contributing an article on the benefits of coldframes and would really like to use a picture of your coldframe as an illustration. It's very well done. Thank you for your consideration!

Sarah Browning
University of Nebraska- Lincoln Extension
(402) 441-7180
sbrowning2@unl.edu

Send me an IM if you need additional info.