I'm asking a few wood working question in relation to an owl box I'm making to put on my property. My question is about drain holes in this and any bird box.

I've always put drain holes in bird houses I've made, because they've called for them. However, they don't make much sense to me. It seems like any bedding or nesting material would absorb any pee, and there wouldn't be enough to need draining. I'd also think that general debris would clog any drain holes.

Firstly, do you guys think that drain holes are necessary? The only real use I can think of is that they might be for any rain that gets in. However, if nesting material and bird crap get in them and clog them up, they wouldn't even drain that. It seems to me that it'd be more important for air circulation to get rid of any toxic fumes like ammonia from the pee and to evaporate any liquids.

Secondly, if you think they are necessary, how do you recommend doing them. Would you just use holes, slots, or like some I've seen, would you chamfer the corners of the bottom so you have a vent on each corner? Will any liquid even run to these vents or would you need to work the wood to have some kind of slope to direct it to the corner holes? Thanks for the help.

  • Everything I read says you must put drainage holes in the base. This seems pointless to me, because according to all the popular plans I've seen online, I doubt many people are making watertight joints around the base. Surely any rain that gets in would seep out of the joints, unless you actually seal them. Wood may expand in damp conditions, making a tighter join, but in the boxes I've made, there's no way there's not gonna be some gaps. However, I am more concerned about ventillation. I don't want my chicks getting too hot, but then I don't want them getting cold either, which is probably mo
    – Jamie Case
    Commented Mar 6 at 21:03

2 Answers 2


Drain holes are necessary

Obviously the inhabitants of the house still have to get in somehow. Seal it up all you want but they will need an entrance. That entrance would be a means to allow rain to enter (I suppose maybe ambient moisture as well). Yes, you will have an overhang but wind will still push water in. Some styles of house don't have effective overhangs especially larger ones, like bird hotels, where they cannot cover all spaces efficiently. Yours will not be the case.

Urine is not really an issue. Like you said it would most likely be absorbed in the nest.

Depending on your choice of wood sitting water could encourage the wood to rot which you don't want. As mentioned in a Birdhouse Selection Guide mold would also be a concern.

Make sure your birdhouse has drain holes in the bottom to let out water. This is important to keep mold and bacteria from multiplying.

Make your holes

One in each corner would be best so that no matter which orientation of the birdhouse the water can exit somewhere. Small 1/4" holes would be more than sufficient and then let gravity do the work.

Need to be careful though as too many could allow more wind to get in reducing the overall temperature. So don't get all hole happy. Birds might not like that and would either not nest there or could move.


Overall it does seem like a good idea to at least have the one drain hole. This allows for a little air circulation as well. Sure debris would get in there but doubt it makes and air/water tight seal.

Sidenote: Also as a birdhouse owners we are supposed to check for debris and such things after the inhabitants have moved out as part of proper maintenance. This is to extend the houses life.

  • I get most of what you're saying, but some of you're wording confuses me. The first sentence says, "Drain holes are necessary, because the inhabitants still need to get in somehow." Then you say, "That hole would be a means to allow rain to enter." I'm asking about drain holes in the bottom. There would be an entrance, and I wouldn't encourage rain to enter. Also, the wood rotting is hopefully not going to be an issue as I plan to treat it with something safe. I also plan to clean it out every season. I'm mainly asking whether they work as intended and if so, the best way to create them.Thanks
    – Dalton
    Commented Apr 22, 2015 at 19:33
  • @Dalton yeah... sorry about the confusion. There are some thoughts missing here. I will update this.
    – Matt
    Commented Apr 22, 2015 at 19:40
  • @dalton I have tried to make my answer clearer. Hopefully it makes sense to you now as well. Never did good in English class. It always looks right to me.
    – Matt
    Commented Apr 22, 2015 at 19:51
  • That's a clearer answer. You're saying that regardless of how you build it, some rain may get in and the drain holes are for that, more than bird waste. The holes in each corner accommodate for possible tilt of the house. That makes sense to me. Thanks.
    – Dalton
    Commented Apr 22, 2015 at 19:57
  • You're welcome sorry about the roller coaster to get to this point.
    – Matt
    Commented Apr 22, 2015 at 20:03

Holes may be necessary to allow air movement, depending on design and craftsmanship. In the natural world, bird make nests and select houses from a variety of materials, depending on species and habitat. They don't make waterproof, airtight houses or nests. Birds that will nest in your bird house also nest in cavities in trees, formed from damage, cracks, etc. These cavities aren't waterproof nor airtight, but they all share a common feature: the entrance hole size is species specific. Smaller holes keep out larger birds & predators, protecting the nesting eggs- think house wren vs. starling, for example. So, you should research that portion of the design. The material used in the bird house is also important- you want something that can breath- like unfinished wood, not painted, sealed, etc.

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