Friday, December 21, 2012

Cold Frame/Greenhouse/Potting Bench Post 4

The last post closed with the installation of the bench bottom.  I mentioned that gaps were left on the edges so water could drain off.  Here’s a photo showing the gaps, about 1/8 inch.  The 2 x 2 supports underneath have grooves on the side attached to the 1 x 8 bandboard.  Hopefully moisture can find its way out through these channels so it does not build up inside the greenhouse. 

With some more cedar 2 x 4’s on hand (boy that stuff is pricey) the project moved on.  The 2 x 4’s were ripped on the table saw into 2 x 2’s and used to make the bottom shelf frame.  Later I’ll put 1 x 2 crosspieces across the frame spaced about 2 inches apart to complete the shelf.  The temporary frame was removed.  I cut 1 inch off of each leg to lower the bench height a little.  Then a 2 x 2 ridge was attached between the top of the back legs. 

The little greenhouse at this point is a very rigid structure, a fact that pleases me greatly.    Rigidity translates to strength.  In fact I stepped up onto the bench and walked on it (that’s 180 lbs) – solid as a rock!  I’m confident that I can put bricks,  limestone pieces and large pots on the bench for thermal mass with no problems. 
Next the back wall went on.  First a piece of aluminum drip edge was installed over the back 1 x 8 to keep water from entering the unit.   

The top piece of siding was ripped at a 35 degree angle on the table saw to follow the angle of the 2 x 2 ridge.  The angles used are either 35 or 55 degrees.  For those of you who remember that class in plane geometry you took in high school, the two angles of a right triangle that are not the 90 degree angle always add up to 90 degrees.  The front of the greenhouse will face 35 degrees above the horizon – a good angle to catch the low winter sun. 

Here’s a view of the front of the greenhouse.  The aluminum drip edge stands out.  That’s OK because when the greenhouse is together I will staple Reflectix insulation onto the back wall.  That’s the stuff that looks like silvered bubble wrap.  It will not only bump up the R-value of the growing space but it has 97% reflectivity.  That should amplify the weak winter sun. 

The most challenging job is ahead – building the hinged lid that holds the twinwall polycarbonate panels .  I’m still trying to work out a design that will effectively keep weather out.  It looks like I’ll have to attach some hinges to some short wood blocks and try to model the real thing.  That means working in a cold pole barn as the winter storm is winding down.  Brrrrrr.   
(Apologies for the mixed fonts.  Blogger is being a pain today).      

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