But what are the out of pocket costs? You can't deduct personal expenses, so at best you would have to follow the exclusivity rule for the home office deduction and set aside a space, room or part of a room, that is used only for the charity work. And then you can use the square footage to figure out the electric, gas and so on that are attributed to that space.
But then you're going to run up against the no partial interest rule. You can't deduct a partial interest in property -- for example, you own a lakeside home and donate its use for a week for a leadership conference. You can't deduct the donation, even if it would have a fair market value as a rental. Or you buy a computer to do your charity work -- its not a deductible donation unless the charity gets full rights and title to the computer, meaning they could take it from your home any time they wanted to, and if you stop working for the charity, the charity keeps the computer. If you keep it, it's only a donation of a partial interest and not deductible. So I can't see how you could even take a deduction for mortgage payment or property taxes even using the square foot method, since that amounts to a partial interest in the home. At best, you could deduct gas and electric, since that's used up.
Thinking more about that, what if you have a freezer you use exclusively to store food for a charity food bank, and you have a separate electric meter; then I think you could deduct the out of pocket cost of the electricity. Here, that might be a possibility (if you follow the exclusivity rules), but I think it would be a stretch, since there is nothing like a home office provision relating to charity donations.
[Edited to add] At best, you might be able to donate expenses that are "used up" since the charity gets the full use of the expense. Other than office supplies and similar things, that might include gas and electricity, but I can't see it including carpet, furniture, mortgage or other household expenses that are otherwise included in a home office deduction, and certainly not depreciation.
