When working from home you can claim a proportion of common expenses - ESB, gas, telephone, insurances - as allowable expenses. How you calculate this should be clearly set out eg. 1 room used in 5 room property = claim 1/5 of expenses. I think it is possible to claim on a time basis as well - best to have a chat with the Revenue, they're generally very helpful.
You should be aware that if you sell your house, then you may become liable to pay Capital Gains tax on that element of your home on which you were claiming the business expenses. When you've calculated the proportion of the expenses you want to claim, it would be worth doing a cross check on what your Capital Gains tax liability would be, to see if claiming expenses is a short term gain leading to a long term loss.